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# College Physics 2013

## Educators

SE  LB + 2 more educators

### Problem 1

You and a friend are playing tennis. (a) What is the magnitude of the momentum of the 0.057-kg tennis ball when it travels at a speed of 30 m/s? (b) At what speed must your 0.32-kg tennis racket move to have the same magnitude momentum as the ball? (c) If you run toward the ball at a speed of 5.0 m/s,
and the ball is flying directly at you at a speed of 30 m/s, what is the magnitude of the total momentum of the system (you and the ball)? Assume your mass is 60 kg. In every case specify the object of reference.

SE
Steven E.
University of California - Los Angeles

### Problem 2

You are hitting a tennis ball against a wall. The 0.057-kg tennis ball traveling at 25 m/s strikes the wall and rebounds at the same speed. (a) Determine the ball’s original momentum (magnitude and direction). (b) Determine the ball’s change in momentum (magnitude and direction). What is your object of reference?

SE
Steven E.
University of California - Los Angeles

### Problem 3

A ball of mass m and speed v travels horizontally, hits a wall, and rebounds. Another ball of the same mass and traveling at the same speed hits the wall and sticks to it. Which ball has a greater change in momentum as a result of the collision? Explain your answer.

SE
Steven E.
University of California - Los Angeles

### Problem 4

(a) A 145-g baseball travels at 35 m/s toward a baseball player’s bat (the bat is the object of reference) and rebounds in the opposite direction at 40 m/s. Determine the ball’s momentum change (magnitude and direction). (b) A golfer hits a 0.046-kg golf ball that launches from the grass at a speed of 50 m/s.
Determine the ball’s change in momentum.

SE
Steven E.
University of California - Los Angeles

### Problem 5

A 1300-kg car is traveling at a speed of 10 m/s with respect to the ground when the driver accelerates to make a green light. The momentum of the car increases by 12,800 kg # m > s. List all the quantities you can determine using this information and determine three of those quantities.

SE
Steven E.
University of California - Los Angeles

### Problem 6

The rules of tennis specify that the 0.057-kg ball must bounce to a height of between 53 and 58 inches when dropped from a height of 100 inches onto a concrete slab. What is the change in the momentum of the ball during the collision with the concrete? You will have to use some free-fall kinematics to help answer this question. Aaron S.

### Problem 7

A cart of mass m moving right at speed v with respect to the track collides with a cart of mass 0.7m moving left. What is the initial speed of the second cart if after the collision the carts stick together and stop?

SE
Steven E.
University of California - Los Angeles

### Problem 8

A cart of mass m moving right collides with an identical cart moving right at half the speed. The carts stick together. What is their speed after the collision?

SE
Steven E.
University of California - Los Angeles

### Problem 9

EST Estimate your momentum when you are walking at your normal pace.

Check back soon!

### Problem 10

A 100-g apple is falling from a tree. What is the impulse that Earth exerts on it during the first 0.50 s of its fall? The next 0.50 s? Eric M.

### Problem 11

The same 100-g apple is falling from the tree. What is the impulse that Earth exerts on it during the first 0.50 m of its fall? The next 0.50 m? Eric M.

### Problem 12

Why does Earth exert the same impulse during the two time intervals in Problem 10 but different impulses during the same distances traveled in Problem 11? Eric M.

### Problem 13

Van hits concrete support In a crash test, a van collides with a concrete support. The stopping time interval for the collision is 0.10 s, and the impulse exerted by the support on the van is $7.5 \times 10^{3} {N} \cdot {s}$ (a) Determine everything you can about the collision using this information. (b) If the van is constructed to collapse more during the collision so that the time interval during which the impulse is exerted is tripled, what is the average force exerted by the concrete support on the van? Eric M.

### Problem 14

BIO Force exerted by heart on blood About 80 g of blood is pumped from a person’s heart into the aorta during each heartbeat. The blood starts at rest with respect to the body and has a speed of about 1.0 m/s in the aorta. If the pumping takes 0.17 s, what is the magnitude of the average force exerted by the heart on the blood? Eric M.

### Problem 15

The train tracks on which a train travels exert a $2.0 \times 10^{5} {N}$ friction force on the train, causing it to stop in 50 s. (a) Determine the average force needed to stop the train in 25 s.(b) Determine the stopping time interval if the tracks exert a $1.0 \times 10^{5}-{N}$ friction force on the train. Eric M.

### Problem 16

EST Your friend is catching a falling basketball after it has passed through the basket. Her hands move straight down 0.20 m while catching the ball. Estimate (a) the time interval for the ball to stop as she catches it and (b) the average force that her hands exert on the ball while catching it. Indicate any
assumptions or estimates you have to make in order to answer the questions.

Check back soon!

### Problem 17

BIO Traumatic brain injury According to a report on traumatic brain injury, the force that a professional boxer’s fist exerts on his opponent’s head is equivalent to being hit with a 5.9 kg bowling ball traveling at 8.9 m/s that stops in 0.018 s. Determine the average force that the fist exerts on the head. Eric M.

### Problem 18

A 65-kg astronaut pushes against the inside back wall of a 2000-kg spaceship and moves toward the front. Her speed increases from 0 to 1.6 m/s. (a) If her push lasts 0.30 s, what is the average force that the astronaut exerts on the wall of the spaceship? (b) If the spaceship was initially at rest, with what
speed does it recoil? (c) What was the object of reference that you used to answer parts (a) and (b)? Eric M.

### Problem 19

You decide to use your garden hose to wash your garage door. The water shoots out at a rate of 10 kg/s and a speed of 16 m/s with respect to the hose. When the water hits the garage, its speed decreases to zero. Determine the force that the water exerts on the wall. What assumptions did you make? Eric M.

### Problem 20

The air in a windstorm moves at a speed of 30 m/s. When it hits a stop sign, the air stops momentarily. The mass of air hitting the stop sign each second is about 2.0 kg. Make a list of physical quantities you can determine using this information and determine three of them. Eric M.

### Problem 21

An egg rolls off a kitchen counter and breaks as it hits the floor. How large is the impulse that the floor exerts on the egg, and how large is the force exerted on the egg by the floor when stopping it? The counter is 1.0 m high, the mass of the egg is about 50 g, and the time interval during the collision is Eric M.

### Problem 22

Retractable car bumper A car bumper exerts an average force on a car as it retracts a certain distance during a collision. Using the impulse-momentum equation, show that the magnitude of the force and the retraction distance are related by the equation $F \Delta x=0.5 m v_{0}^{2}$ What assumptions did you
make? Eric M.

### Problem 23

Proportional reasoning Use proportional reasoning and the equation from Problem 22 to determine (a) the necessary percent change in the retraction distance so that the average force required to stop a car is reduced by 20% and (b) the percent change in initial to final speed that would produce the same
reduction in force. Eric M.

### Problem 24

(a) What force is required to stop a 1500-kg car in a distance of 0.20 m if it is initially moving at 2.2 m/s? (b) What if the car is moving at 4.5 m/s? Eric M.

### Problem 25

A boxer delivers a punch to his opponent’s head, which has a mass of 7.0 kg. Use the graph in Figure P5.25 to estimate (a) the impulse of the force exerted by the boxer and (b) the speed of the head after the punch is delivered. What assumptions did you make?

LB
Liev B.

### Problem 26

Air bag force on head The graph in Figure P5.26 shows the time variation of the force that an automobile’s air bag exerts on a person’s head during a collision. The mass of the head is 8.0 kg. Determine (a) the total impulse of the force exerted by the air bag on the person’s head and (b) the person’s speed just be- fore the collision occurred. Mahmoud A.

### Problem 27

Equation Jeopardy 1 Invent a problem for which the solution is
$(27 {kg})(-3.0 {m} / {s})+(30 {kg})(+4.0 {m} / {s})=(27 {kg}+30 {kg}) v$ Eric M.

### Problem 28

Equation Jeopardy 2 Invent a problem for which the solution is
$(0.020 {kg})(300 {m} / {s})-(10 {N})(0.40 {s})=(0.020 {kg})(100 {m} / {s})$ Eric M.

### Problem 29

Write a general impulse-momentum equation that describes the following process: a person skating on rollerblades releases a backpack that falls toward the ground (the process ends before the backpack hits the ground). What is the system, and what are the physical quantities you will use to describe the process? Eric M.

### Problem 30

Two carts (100 g and 150 g) on an air track are separated by a compressed spring. The spring is released. Represent the process with a momentum bar chart (a) with one cart as the system and (b) with both carts as the system. (c) Write expressions for all of the physical quantities you can from this
information. Identify your object of reference. Eric M.

### Problem 31

A tennis ball of mass m hits a wall at speed v and rebounds at about the same speed. Represent the process with an impulse-momentum bar chart for the ball as the system. Using the bar chart, develop an expression for the change in the ball’s momentum. What is the object of reference? Eric M.

### Problem 32

A tennis ball traveling at a speed of v stops after hitting a net. Represent the process with an impulse-momentum bar chart for the ball as the system. Develop an expression for the ball’s change in momentum. What is the object of reference? Eric M.

### Problem 33

You drop a happy ball and a sad ball of the same mass from height h (see Example 5.3). One ball hits the ground and rebounds almost to the original height. The other ball does not bounce. Represent each process with a bar chart, starting just before the balls hit the ground to just after the first ball rebounds
and when the other ball stops. Choose the ball as the system. Eric M.

### Problem 34

You experiment again with the balls from Problem 33. You drop them from the same height onto a ruler that is placed on the edge of a table (Figure P5.34). One ball knocks the ruler off; the other does not. Represent each process with an impulse-momentum bar chart with (a) the ball as a system and (b) the ball and the ruler as the system. The process starts just before the balls hit the ruler and ends immediately after they hit the ruler. Use the bar charts to help explain the difference in the results of the
experiment. Eric M.

### Problem 35

You demonstrate hitting a board in a karate class. The speed of your hand as it hits the thick board is 14 m/s with respect to the board, and the mass of your hand is about 0.80 kg. How deep does your hand go into the board before stopping if the collision lasts for $2.0 \times 10^{-3} {s} ?$ What assumptions did you make? What other quantities can you determine using this information? Eric M.

### Problem 36

You hold a beach ball with your arms extended above your head and then throw it upward. Represent the motion of the ball with an impulse-momentum bar chart for (a) the ball as the system and (b) the ball and Earth as the system. Eric M.

### Problem 37

A basketball player drops a 0.60-kg basket- ball vertically so that it is traveling at 6.0 m/s when it reaches the floor. The ball rebounds upward at a speed of 4.2 m/s. (a) Determine the magnitude and direction of the ball’s change in momentum. (b) Determine the average net force that the floor exerts on the ball if the collision lasts 0.12 s. Eric M.

### Problem 38

Bar chart Jeopardy Invent a problem for each of the bar charts shown in Figure P5.38. Eric M.

### Problem 39

A baseball bat contacts a 0.145-kg baseball for $1.3 \times 10^{-3}$ s. The average force exerted by the bat on the ball is 8900 N. If the ball has an initial velocity of 36 m/s toward the bat and the force of the bat causes the ball’s motion to reverse direction, what is the ball’s speed as it leaves the bat? Eric M.

### Problem 40

A tennis ball traveling horizontally at a speed of 40.0 m/s hits a wall and rebounds in the opposite direction. The time interval for the collision is about 0.013 s, and the mass of the ball is 0.059 kg. Make a list of quantities you can determine using this information and determine four of them. Assume that the ball rebounds at the same speed. Eric M.

### Problem 41

A cannon mounted on the back of a ship fires a 50-kg cannonball in the horizontal direction at a speed of 150 m/s. If the cannon and ship have a combined mass of 40000 kg and are initially at rest, what is the speed of the ship just after shooting the cannon? What assumptions did you make? Eric M.

### Problem 42

A team in Quebec is playing ice baseball. A 72-kg player who is initially at rest catches a 145-g ball traveling at 18 m/s. If the player’s skates are frictionless, how much time is required for him to glide 5.0 m after catching the ball? Eric M.

### Problem 43

A 10-kg sled carrying a 30-kg child glides on a horizontal, frictionless surface at a speed of 6.0 m/s toward the east. The child jumps off the back of the sled, propelling it forward at 20 m/s. What was the child’s velocity in the horizontal direction relative to the ground at the instant she left the sled? Eric M.

### Problem 44

A 10,000-kg coal car on the Great Northern Railroad coasts under a coal storage bin at a speed of 2.0 m/s. As it goes under the bin, 1000 kg of coal is dropped into the car. What is the final speed of the loaded car? Hamza Z.

### Problem 45

Avoiding chest injury A person in a car during a sudden stop can experience potentially serious chest injuries if the combined force exerted by the seat belt and shoulder strap exceeds 16,000 N. Describe what it would take to avoid injury by estimating (a) the minimum stopping time interval and (b) the corresponding stopping distance, assuming an initial speed of 16 m/s. Indicate any other assumptions you made. Eric M.

### Problem 46

Bruising apples An apple bruises if a force greater than 8.0 N is exerted on it. Would a 0.10-kg apple be likely to bruise if it falls 2.0 m and stops after sinking 0.060 m into the grass? Explain. Eric M.

### Problem 47

Fast tennis serve The fastest server in women’s tennis is Venus Williams, who recorded a serve of 204 km/h at the French Open in 2007. Suppose that the mass of her racket was 328 g and the mass of the ball was 57 g. If her racket was moving at 200 km/h when it hit the ball, approximately what was the racket’s speed after hitting the ball? Indicate any assumptions you made. Eric M.

### Problem 48

You are in an elevator whose cable has just broken. The elevator is falling at 20 m/s when it starts to hit a shock-absorbing device at the bottom of the elevator shaft. If you are to avoid injury, the upward force that the floor of the elevator exerts on your upright body while stopping should be no more than 8000 N. Determine the minimum stopping distance needed to avoid injury (do not forget to include your
mass in the calculations). What assumptions did you make? Do these assumptions make the stopping distance smaller or larger than the real-world value? Eric M.

### Problem 49

You jump from the window of a burning hotel and land in a safety net that stops your fall in 1.0 m. Estimate the average force that the net exerts on you if you enter the net at a speed of 24 m/s. What assumptions did you make? If you did not make these assumptions, would the stopping distance be
smaller or larger? Eric M.

### Problem 50

Skid marks A car skids to a stop. The length of the skid marks is 50 m. What information do you need in order to decide whether the car was speeding before the driver hit the brakes? Eric M.

### Problem 51

BIO Leg injuries during car collisions During a car collision, the knee, thighbone, and hip can sustain a force no greater than 4000 N. Forces that exceed this amount could cause dislocations or fractures. Assume that in a collision a knee stops when it hits the car’s dashboard. Also assume that the mass of the body parts stopped by the knee is about 20% of the total body mass. (a) What minimum stopping time interval in needed to avoid injury to the knee if the person is initially traveling at 15 m/s (34 mi/h)? (b) What is the minimum stopping distance? Eric M.

### Problem 52

BIO Bone fracture The zygomatic bone in the upper part of the cheek can be fractured by a 900-N force lasting 6.0 ms or longer. A hockey puck can easily exert such a force when hitting an unprotected face. (a) What change in velocity of a 0.17-kg hockey puck is needed to provide that impulsive force? What assumptions did you make? (b) A padded face-mask doubles the stopping time. By how much does it change the force on the face? Explain. Eric M.

### Problem 53

An impulse of 150 N # s stops your head during a car collision. (a) A crash test dummy’s head stops in 0.020 s, when the cheekbone hits the steering wheel. What is the average force that the wheel exerts on the dummy’s cheekbone? (b) Would this crash fracture a human cheekbone (see Problem 52)?
(c) What is the shortest impact time that a person could sustain without breaking the bone? Eric M.

### Problem 54

A cart is moving on a horizontal track when a heavy bag falls vertically onto it. What happens to the speed of the cart? Represent the process with an impulse-momentum bar chart. Eric M.

### Problem 55

A cart is moving on a horizontal track. A heavy bag falls off the cart and moves straight down relative to the cart. Describe what happens to the speed of the cart. Represent your answer with the impulse-momentum bar chart. [Hint: What reference frame will you use when you draw the bar chart?] Eric M.

### Problem 56

Your friend shoots an 80-g arrow through a 100-g apple balanced on William Tell’s head. The arrow has a speed of 50 m/s before passing through the apple and 40 m/s after. Determine the final speed of the apple. Eric M.

### Problem 57

BIO Potassium decay in body tissue Certain natural forms of potassium have nuclei that are radioactive. Each radioactive potassium nucleus decays to a slightly less massive daughter nucleus and a high-speed electron called a beta particle. If after the decay the daughter nucleus is moving at speed 200 m/s
with respect to the decaying material, how fast is the electron (the beta particle) moving? Indicate any assumptions you made. The mass of the daughter is about 70,000 times greater than the mass of the beta particle. Eric M.

### Problem 58

Meteorite impact with Earth About 65 million years ago a 10 -km-diameter $2 \times 10^{15}$ -kg meteorite traveling at about 10 ${km} / {s}$ crashed into what is now the Gulf of Mexico. The impact produced a cloud of debris that darkened Earth and led to the extinction of the dinosaurs. Estimate the speed Earth gained as a result of this impact and the average force that the meteorite exerted on Earth during the collision. Indicate any Eric M.

### Problem 59

Three friends play beach volleyball. The 280 g ball is flying east at speed 8.0 m/s with respect to the ground when one of the players bumps the ball north. The force exerted by the wrist on the ball has an average magnitude of 84 N and lasts for 0.010 s. Determine the ball’s velocity (magnitude and direction) following the bump. Does your answer make sense? Eric M.

### Problem 60

Car collision A 1180-kg car traveling south at 24 m/s with respect to the ground collides with and attaches to a 2470-kg delivery truck traveling east at 16 m/s. Determine the velocity (magnitude and direction) of the two vehicles when locked together just after the collision. Eric M.

### Problem 61

Ice skaters collide While ice skating, you unintentionally crash into a person. Your mass is 60 kg, and you are traveling east at 8.0 m/s with respect to the ice. The mass of the other person is 80 kg, and he is traveling north at 9.0 m/s with respect to the ice. You hang on to each other after the collision. In what direction and at what speed are you traveling just after the collision? Eric M.

### Problem 62

Drifting space mechanic An astronaut with a mass of 90 kg (including spacesuit and equipment) is drifting away from his spaceship at a speed of 0.20 m/s with respect to the spaceship. The astronaut is equipped only with a 0.50-kg wrench to help him get back to the ship. With what speed and in what direction relative to the spaceship must he throw the wrench for his body to acquire a speed of 0.10 m/s and direct him back toward the spaceship? Explain. Eric M.

### Problem 63

Astronaut flings oxygen tank While the astronaut in Problem 62 is trying to get back to the spaceship, his comrade, a 60-kg astronaut, is floating at rest a distance of 10 m from the spaceship when she runs out of oxygen and fuel to power her back to the spaceship. She removes her oxygen tank (3.0 kg) and flings it away from the ship at a speed of 15 m/s relative to the ship. (a) At what speed relative to the ship does she recoil toward the spaceship? (b) How long must she hold her breath before reaching the ship? Eric M.

### Problem 64

Rocket stages A 5000-kg rocket ejects a 10,000-kg package of fuel. Before ejection, the rocket and the fuel travel together at a speed of 200 m/s with respect to distant stars. If after the ejection, the fuel package travels at 50 m/s opposite the direction of its initial motion, what is the velocity of the rocket? Ethan L.

### Problem 65

A rocket has just ejected fuel. With the fuel and the rocket as the system, construct an impulse-momentum bar chart for (a) the rocket’s increase in speed and (b) the process of a rocket slowing down due to fuel ejection. (c) Finally, draw bar charts for both situations using the rocket without the fuel as
the system. Eric M.

### Problem 66

You have two carts, a force probe connected to a computer, a motion detector, and an assortment of objects of different masses. Design three experiments to test whether momentum is a conserved quantity. Describe carefully what data you will collect and how you will analyze the data. Eric M.

### Problem 67

EST Estimate the recoil speed of Earth if all of the inhabitants of Canada and the United States simultaneously jumped straight upward from Earth’s surface (reaching heights from several centimeters to a meter or more). Indicate any assumptions that you made in your estimate.

Check back soon!

### Problem 68

A cart of mass m traveling in the negative x-direction at speed v collides head-on with a cart that has triple the mass and is moving at 60% of the speed of the first cart. The carts stick together after the collision. In which direction and at what speed will they move? Eric M.

### Problem 69

Two cars of unequal mass moving at the same speed collide head-on. Explain why a passenger in the smaller mass car is more likely to be injured than one in the larger mass car. Justify your reasoning with the help of physics principles. Eric M.

### Problem 70

Restraining force during collision A 1340-kg car traveling east at 13.6 m/s (20 mi/h) has a head-on collision with a 1930-kg car traveling west at 20.5 m/s (30 mi/h). If the collision time is 0.10 s, what is the force needed to restrain a 68-kg person in the smaller car? In the larger car? Eric M.

### Problem 71

EST A carpenter hammers a nail using a 0.40-kg hammerhead. Part of the nail goes into a board. (a) Estimate the speed of the hammerhead before it hits the nail. (b) Estimate the stopping distance of the hammerhead. (c) Estimate the stopping time interval. (d) Estimate the average force that the hammerhead exerts on the nail. Eric M.

### Problem 72

A 0.020-kg bullet traveling at a speed of 300 m/s embeds in a 1.0-kg wooden block resting on a horizontal surface. The block slides horizontally 4.0 m on a surface before stopping. Determine the coefficient of kinetic friction between the block and surface. Eric M.

### Problem 73

EST Nolan Ryan may be the fastest baseball pitcher of all time. The Guinness Book of World Records clocked his fastball at 100.9 mi/h in a 1974 game against the Chicago White Sox. Use the impulse-momentum equation to estimate the force that Ryan exerted on the ball while throwing that pitch. Include any assumptions you made. Eric M.

### Problem 74

A record rainstorm produced 304.8 mm (approximately 1 ft) of rain in 42 min. Estimate the average force that the rain exerted on the roof of a house that measures 10 m * 16 m. Indicate any assumptions you made. Eric M.

### Problem 75

EST The U.S. Army special units MH-47E helicopter has a mass of 23,000 kg, and its propeller blades sweep out an area of 263 ${m}^{2}$. It is able to hover at a fixed elevation above one landing point by pushing air downward (the air pushes up on the helicopter blades). Choose a reasonable air mass displaced downward each second and the speed of that air in order for the helicopter to hover. Indicate any assumptions you made. Eric M.

### Problem 76

A 2045-kg sports utility vehicle hits the rear end of a 1220-kg car at rest at a stop sign. The car and SUV remain locked together and skid 4.6 m before stopping. If the coefficient of friction between the vehicles and the road is 0.70, what was the SUV’s initial velocity? Eric M.

### Problem 77

A car of mass $m_{1}$ traveling north at a speed of $v_{1}$ collides with a car of mass $m_{2}$ traveling east at a speed of $v_{2}$ . They lock together after the collision. Develop expressions for the direction and the distance the cars will move until they stop if the coefficient of kinetic friction $\mu_{{k}}$ between the cars' tires and the road is about the same for both cars. Eric M.

### Problem 78

Force exerted by wind on Willis Tower A 10.0-m/s wind blows against one side of the Willis Tower in Chicago. The building is 443 m tall and approximately 80 m wide. Estimate the average force of the air on the side of the building. The density of air is approximately 1.3 ${kg} / {m}^{3}$ . Indicate any assumptions that you made. Eric M.

### Problem 79

Write your own problem. Write and solve a problem that requires using the law of conservation of momentum in which it is important to know that momentum is a vector quantity. Eric M.

### Problem 80

What does the heartbeat detector sense?
(a) Electric signals caused by electric dipole charges produced on the heart
(b) Body vibrations caused by blood pumped from the heart
(c) Sound caused by breathing
(d) Slight uncontrollable reflexive motions of an enclosed person
(e) All of the above Eric M.

### Problem 81

A heartbeat detector relies on a geophone placed against the exterior of a truck or car. What can cause the vibrations of the truck or car?
(a) Wind
(b) Ground vibrations due to other moving cars or trucks
(c) Vibrations of passengers in the car or truck
(d) All of the above Eric M.

### Problem 82

What can be used to analyze the motion of a person’s body hidden inside a car or truck (choosing the body and blood as a system)?
(a) The idea that mass of an isolated system is constant
(b) The idea that momentum of an isolated system is constant
(c) The impulse-momentum principle
(d) a and b
(e) b and c Eric M.

### Problem 83

During each heartbeat, about 0.080 kg of blood passes the aorta in about 0.16 s. This blood’s velocity changes from about 0.8 m/s upward toward the head to 0.8 m/s down toward the feet. What is the blood’s acceleration?
(a) 0.0009 ${m} / {s}$ (b) 0.002 ${m} / {s}$ (c) 0.8 ${m} / {s}$
(d) 10 ${m} / {s}^{2} {up} (e) 10 {m} / {s}^{2} {down}$ Eric M.

### Problem 84

Suppose 0.080 kg of blood moving upward in the aorta at 0.8 m/s reverses direction in 0.16 s when it reaches the aortic arch. If a prisoner is trying to escape from prison by hiding in a laundry truck, and the mass of his body is 70 kg, which is the closest to the speed his body is moving immediately after the
blood changes direction passing through the aortic arch?
(a) 0.0009 ${m} / {s}$ (b) 0.002 ${m/s}$ (c) 0.8 ${m} / {s}$
(d) 0.08 ${m} / {s}$ (e) 0.01 ${m} / {s}$ Eric M.

### Problem 85

Which number below is closest to the acceleration of the shuttle during liftoff? [Hint: Remember the gravitational force that Earth exerts on the shuttle.]
(a) $3.3 {m} / {s}^{2}$ (b) $6.6 {m} / {s}^{2}$ (c) $9.8 {m} / {s}^{2}$
(d) 16 ${m} / {s}^{2}$ (e) 33 ${m} / {s}^{2}$ Eric M.

### Problem 86

Which number below is closest to the average vertical acceleration of the shuttle during the first 132 s of its flight?
(a) 3.3 ${m} / {s}^{2}$ (b) 6.6 ${m} / {s}^{2}$ (c) 9.8 ${m} / {s}^{2}$
(d) 16 ${m} / {s}^{2}$ (e) 33 ${m} / {s}^{2}$

Check back soon!

### Problem 87

The boosters are released from the shuttle 132 s after launch. How do their vertical components of velocity compare to that of the shuttle at the instant of release?
(a) The boosters’ vertical component of velocity is zero.
(b) The boosters’ vertical component of velocity is about -9.8 m/s.
(c) The vertical component of velocity of the boosters and that of the Shuttle are the same.
(d) There is too little information to decide. Eric M.

### Problem 88

What is the approximate impulse of the jet engine thrust exerted on the shuttle during the first 10 s of flight?
(a) 980 ${N} \cdot$ s downward
(b) 980 ${N} \cdot$ s upward
(c) $2.1 \times 10^{7} {N} \cdot$ s upward
(d) $2.1 \times 10^{8} {N} \cdot$ s upward
(e) $2.1 \times 10^{8} {N} \cdot$ s downward Eric M.

### Problem 89

What is the approximate impulse of Earth's gravitational force exerted on the shuttle during the first $10 \mathrm{~s}$ of flight?
(a) $980 \mathrm{~N} \cdot \mathrm{s}$ downward
(b) $980 \mathrm{~N} \cdot \mathrm{s}$ upward
(c) $2.1 \times 10^{7} \mathrm{~N} \cdot \mathrm{s}$ upward
(d) $2.1 \times 10^{8} \mathrm{~N} \cdot \mathrm{s}$ upward
(e) $2.1 \times 10^{8} \mathrm{~N} \cdot \mathrm{s}$ downward Eric M.

### Problem 90

What is the momentum of the Space Shuttle 10 s after liftoff closest to?
(a) $2.1 \times 10^{6} {kg} \cdot {m} / {s}$ down $\quad$ (b) $2.1 \times 10^{6} {kg} \cdot {m} / {s}$ up
(c) $2.1 \times 10^{7} {kg} \cdot {m} / {s}$ up $\quad$ (d) $1.3 \times 10^{8} {kg} \cdot {m} / {s}$ up
(e) $1.3 \times 10^{8} {kg} \cdot {m} / {s}$ down Eric M.
What answer below is closest to the speed of the shuttle and boosters when they are released? Assume that the free-fall gravitational acceleration at this elevation is about 9.6 ${m} / {s}^{2}$ down. 