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Essential University Physics

Richard Wolfson

Chapter 5

Using Newton’s Laws - all with Video Answers

Educators


Chapter Questions

01:57

Problem 1

Compare the net force on a heavy trunk when it's (a) at rest on the floor; (b) being slid across the floor at constant speed;
(c) being pulled upward in an elevator whose cable tension equals the combined weight of the elevator and trunk; and
(d) sliding down a frictionless ramp.

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
01:22

Problem 2

The force of static friction acts only between surfaces at rest. Yet that force is essential in walking and in accelerating or braking a car. Explain.

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
02:10

Problem 3

A jet plane flies at constant speed in a vertical circular loop. At what point in the loop does the seat exert the greatest force on the pilot? The least force?

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
02:32

Problem 4

In cross-country skiing, skis should easily glide forward but should remain at rest when the skier pushes back against the snow. What frictional properties should the ski wax have to achieve this goal?

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
01:15

Problem 5

Why do airplanes bank when turning?

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
01:43

Problem 6

Why is it easier for a child to stand nearer the inside of a rotating merry-go-round?

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
01:21

Problem 7

Gravity pulls a satellite toward Earth's center. So why doesn't the satellite actually fall to Earth?

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
02:26

Problem 8

Explain why a car with ABS brakes can have a shorter stopping distance.

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
00:56

Problem 9

A fishing line has a $20-1 b$ breaking strength. Is it possible to break the line while reeling in a 15 -lb fish? Explain.

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
02:03

Problem 10

Two blocks rest on slopes of unequal angles, connected by a rope passing over a pulley (Fig. 5.30). If the blocks have equal masses, will they remain at rest? Why? Neglect friction.

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
02:18

Problem 11

You're on a plane undergoing a banked turn, so steep that out the window you see the ground below. Yet your pretzels stay put on the seatback tray, rather than sliding downward. Why?

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
02:16

Problem 12

A backcountry skier weighing $700 \mathrm{N}$ skis down a steep slope, unknowingly crossing a snow bridge that spans a deep, hidden crevasse. If the bridge can support $580 \mathrm{N}-$ meaning that's the maximum normal force it can sustain without collapsing- is there any chance the mountaineer can cross safely? Explain.

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
02:15

Problem 13

Two forces, both in the $x$ -y plane, act on a $3.25-$ kg mass that accelerates at $5.48 \mathrm{m} / \mathrm{s}^{2}$ in a direction $38.0^{\circ}$ counterclockwise from the $x$ -axis. One force has magnitude $8.63 \mathrm{N}$ and points in the $x-$ direction. Find the other force.

Nicholas Mogoi
Nicholas Mogoi
Numerade Educator
02:30

Problem 14

Two forces act on a 3.1 -kg mass that undergoes acceleration $\vec{a}=0.91 \hat{\imath}-0.27 \hat{\jmath} \mathrm{m} / \mathrm{s}^{2} .$ If one force is $-1.2 \hat{\imath}-2.5 \hat{\jmath} \mathrm{N},$ what's the other?

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
01:26

Problem 15

At what angle should you tilt an air table to simulate free fall at the surface of Mars, where $g=3.71 \mathrm{m} / \mathrm{s}^{2} ?$

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
02:25

Problem 16

A skier starts from rest at the top of a $24^{\circ}$ slope $1.3 \mathrm{km}$ long. Neglecting friction, how long does it take to reach the bottom?

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
01:52

Problem 17

A tow truck is connected to a 1400 -kg car by a cable that makes a $25^{\circ}$ angle to the horizontal. If the truck accelerates at $0.57 \mathrm{m} / \mathrm{s}^{2}$ what's the magnitude of the cable tension? Neglect friction and the cable's mass.

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
01:59

Problem 18

Studies of gymnasts show that their high rate of injuries to the Achilles tendon is due to tensions in the tendon that typically reach 10 times body weight. That force is provided by a pair of muscles, each exerting a force at $25^{\circ}$ to the vertical, with their horizontal components opposite. For a 55 -kg gymnast, find the force in each of these muscles.
CAN'T COPY THE FIGURE

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
01:39

Problem 19

Find the minimum slope angle for which the skier in Question 12 can safely traverse the snow bridge.

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
02:42

Problem 20

Your $12-\mathrm{kg}$ baby sister pulls on the bottom of the tablecloth with all her weight. On the table, $60 \mathrm{cm}$ from the edge, is a $6.8-\mathrm{kg}$ roast turkey. (a) What's the turkey's acceleration? (b) From the time your sister starts pulling, how long do you have to intervene before the turkey goes over the edge? Neglect friction.

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
01:54

Problem 21

If the left-hand slope in Fig. 5.30 makes a $60^{\circ}$ angle with the horizontal, and the right-hand slope makes a $20^{\circ}$ angle, how should the masses compare if the objects are not to slide along the frictionless slopes?

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
03:25

Problem 22

Suppose the angles shown in Fig. 5.30 are $60^{\circ}$ and $20^{\circ} .$ If the left-hand mass is $2.1 \mathrm{kg},$ what should the right-hand mass be so that it accelerates (a) downslope at $0.64 \mathrm{m} / \mathrm{s}^{2}$ and (b) upslope at $0.76 \mathrm{m} / \mathrm{s}^{2} ?$

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
02:51

Problem 23

Two unfortunate climbers, roped together, are sliding freely down an icy mountainside. The upper climber (mass $75 \mathrm{kg}$ ) is on a slope at $12^{\circ}$ to the horizontal, but the lower climber (mass $63 \mathrm{kg}$ ) has gone over the edge to a steeper slope at $38^{\circ} .$ (a) Assuming frictionless ice and a massless rope, what's the acceleration of the pair? (b) The upper climber manages to stop the slide with an ice ax. After the climbers have come to a complete stop, what force must the ax exert against the ice?

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
01:32

Problem 24

Suppose the Moon were held in its orbit not by gravity but by tension in a massless cable. Estimate the magnitude of the cable tension. (Hint: See Appendix E.)

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
01:07

Problem 25

Show that the force needed to keep a mass $m$ in a circular path of radius $r$ with period $T$ is $4 \pi^{2} \mathrm{mr} / T^{2}$.

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
02:28

Problem 26

A $940-\mathrm{g}$ rock is whirled in a horizontal circle at the end of a 1.30-m-long string. (a) If the breaking strength of the string is $120 \mathrm{N},$ what's the minimum angle the string can make with the horizontal? (b) At this minimum angle, what's the rock's speed?

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
02:46

Problem 27

You're investigating a subway accident in which a train derailed while rounding an unbanked curve of radius $150 \mathrm{m},$ and you're asked to estimate whether the train exceeded the $35-\mathrm{km} / \mathrm{h}$ speed limit for this curve. You interview a passenger who had been standing and holding onto a strap; she noticed that an unused strap was hanging at about a $15^{\circ}$ angle to the vertical just before the accident. What do you conclude?

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
02:06

Problem 28

A tetherball on a 1.55 -m rope is struck so that it goes into circular motion in a horizontal plane, with the rope making a $12.0^{\circ}$ angle to the horizontal. What's the ball's speed?

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
01:50

Problem 29

An airplane goes into a turn $3.6 \mathrm{km}$ in radius. If the banking angle required is $28^{\circ}$ from the horizontal, what's the plane's speed?

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
01:00

Problem 30

Movers slide a 73 -kg file cabinet along a floor where the coefficient of kinetic friction is $0.81 .$ What's the frictional force on the cabinet?

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
02:10

Problem 31

A hockey puck is given an initial speed of $14 \mathrm{m} / \mathrm{s}$. If it comes to rest in $56 \mathrm{m},$ what's the coefficient of kinetic friction?

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
04:00

Problem 32

Starting from rest, a skier slides $100 \mathrm{m}$ down a $28^{\circ}$ slope. How much longer does the run take if the coefficient of kinetic friction
is 0.17 instead of $0 ?$

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
05:44

Problem 33

A car moving at $40 \mathrm{km} / \mathrm{h}$ negotiates a $130-\mathrm{m}$ -radius banked turn designed for $60 \mathrm{km} / \mathrm{h} .$ What coefficient of friction is needed to keep the car on the road?

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
03:12

Problem 34

Repeat Example $5.1,$ this time using a horizontal/vertical coordinate system.

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
01:23

Problem 35

A block is launched with initial speed $2.2 \mathrm{m} / \mathrm{s}$ up a $35^{\circ}$ frictionless ramp. How far up the ramp does it slide?

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
01:59

Problem 36

In the process of mitosis (cell division), two motor proteins pull on a spindle pole, each with a 7.3 -pN force. The two force vectors make a $65^{\circ}$ angle. What's the magnitude of the force the two motor proteins exert on the spindle pole?

Supratim Pal
Supratim Pal
Numerade Educator
01:32

Problem 37

A $14.6-\mathrm{kg}$ monkey hangs from the middle of a massless rope, each half of which makes an $11.0^{\circ}$ angle with the horizontal. What's the rope tension? Compare with the monkey's weight.

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
02:58

Problem 38

A camper hangs a $26-\mathrm{kg}$ pack between two trees using separate ropes of different lengths, as shown in Fig. $5.32 .$ Find the tension in each rope.
CAN'T COPY THE FIGURE

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
02:11

Problem 39

A mass $m_{1}$ undergoes circular motion of radius $R$ on a horizontal frictionless table, connected by a massless string through a hole in the table to a second mass $m_{2}$ (Fig. 5.33 ). If $m_{2}$ is stationary,find expressions for (a) the string tension and (b) the period of the circular motion.
CAN'T COPY THE FIGURE

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
01:08

Problem 40

Patients with severe leg breaks are often placed in traction, with an external force countering muscles that would pull too hard on the broken bones. In the arrangement shown in Fig. 5.34 , the mass $m$ is $4.8 \mathrm{kg},$ and the pulleys can be considered massless and frictionless. Find the horizontal traction force applied to the leg.
CAN'T COPY THE FIGURE

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
03:54

Problem 41

Riders on the "Great American Revolution" loop-the-loop roller coaster of Example 5.7 wear seatbelts as the roller coaster negotiates its 6.3 -m-radius loop at $9.7 \mathrm{m} / \mathrm{s} .$ At the top of the loop, what are the magnitude and direction of the force exerted on a $60-\mathrm{kg}$ rider (a) by the roller-coaster seat and (b) by the seatbelt?
(c) What would happen if the rider unbuckled at this point?

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
02:59

Problem 42

A 45 -kg skater rounds a 5.0 -m-radius turn at $6.3 \mathrm{m} / \mathrm{s}$. (a) What are the horizontal and vertical components of the force the ice exerts on her skate blades? (b) At what angle can she lean without falling over?

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
01:55

Problem 43

When a plane turns, it banks as shown in Fig. 5.35 to give the wings' lifting force $\vec{F}_{\mathrm{w}}$ a horizontal component that turns the plane. If a plane is flying level at $950 \mathrm{km} / \mathrm{h}$ and the banking angle $\theta$ is not to exceed $40^{\circ},$ what's the minimum curvature radius for the turn?
CAN'T COPY THE FIGURE

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
01:58

Problem 44

You whirl a bucket of water in a vertical circle of radius $85 \mathrm{cm} .$ What's the minimum speed that will keep the water from falling out?

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
01:31

Problem 45

A child sleds down an $8.5^{\circ}$ slope at constant speed. What's the frictional coefficient between slope and sled?

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
02:27

Problem 46

The handle of a 22 -kg lawnmower makes a $35^{\circ}$ angle with the horizontal. If the coefficient of friction between lawnmower and ground is $0.68,$ what magnitude of force, applied in the direction of the handle, is required to push the mower at constant velocity? Compare with the mower's weight.

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
02:37

Problem 47

Repeat Example $5.4,$ now assuming that the coefficient of kinetic friction between rock and ice is 0.057.

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
01:50

Problem 48

A bat crashes into the vertical front of an accelerating subway train. If the frictional coefficient between bat and train is 0.86 what's the minimum acceleration of the train that will allow the bat to remain in place?

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
02:59

Problem 49

The coefficient of static friction between steel train wheels and steel rails is $0.58 .$ The engineer of a train moving at $140 \mathrm{km} / \mathrm{h}$ spots a stalled car on the tracks $150 \mathrm{m}$ ahead. If he applies the brakes so the wheels don't slip, will the train stop in time?

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
03:35

Problem 50

A bug crawls outward from the center of a CD spinning at 200 revolutions per minute. The coefficient of static friction between the bug's sticky feet and the disc surface is $1.2 .$ How far does the bug get from the center before slipping?

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
04:55

Problem 51

A $310-\mathrm{g}$ paperback book rests on a 1.2 -kg textbook. A force is applied to the textbook, and the two books accelerate together from rest to $96 \mathrm{cm} / \mathrm{s}$ in 0.42 s. The textbook is then brought to a stop in $0.33 \mathrm{s}$ during which time the paperback slides off. Within what range does the coefficient of static friction between the two books lie?

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
03:46

Problem 52

Children sled down a 41 -m-long hill inclined at $25^{\circ} .$ At the bottom, the slope levels out. If the coefficient of friction is $0.12,$ how far do the children slide on the level ground?

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
01:27

Problem 53

In a typical front-wheel-drive car, $70 \%$ of the car's weight rides on the front wheels. If the coefficient of friction between tires and road is $0.61,$ what's the car's maximum acceleration?

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
02:43

Problem 54

A police officer investigating an accident estimates that a moving car hit a stationary car at $25 \mathrm{km} / \mathrm{h}$. Before the collision, the car left 47 -m-long skid marks as it braked. The officer determines that the coefficient of kinetic friction was $0.71 .$ What was the initial speed of the moving car?

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
02:02

Problem 55

A police officer investigating an accident estimates that a moving car hit a stationary car at $25 \mathrm{km} / \mathrm{h}$. Before the collision, the car left 47 -m-long skid marks as it braked. The officer determines that the coefficient of kinetic friction was $0.71 .$ What was the initial speed of the moving car?

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
02:52

Problem 56

You try to move a heavy trunk, pushing down and forward at an angle of $50^{\circ}$ below the horizontal. Show that, no matter how hard you push, it's impossible to budge the trunk if the coefficient of static friction exceeds 0.84.

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
04:20

Problem 57

A block is shoved up a $22^{\circ}$ slope with an initial speed of $1.4 \mathrm{m} / \mathrm{s}$ The coefficient of kinetic friction is $0.70 .$ (a) How far up the slope will the block get? (b) Once stopped, will it slide back down?

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
03:02

Problem 58

At the end of a factory production line, boxes start from rest and slide down a $30^{\circ}$ ramp 5.4 m long. If the slide can take no more than $3.3 \mathrm{s}$, what's the maximum allowed frictional coefficient?

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
04:44

Problem 59

You're in traffic court, arguing against a speeding citation. You entered a 210 -m-radius banked turn designed for $80 \mathrm{km} / \mathrm{h}$, which was also the posted speed limit. The road was icy, yet you stayed in your lane, so you argue that you must have been going at the design speed. But police measurements show there was a frictional coefficient $\mu=0.15$ between tires and road. Is it possible you were speeding, and if so by how much?

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
01:40

Problem 60

A space station is in the shape of a hollow ring, $450 \mathrm{m}$ in diameter (Fig. 5.36 ). At how many revolutions per minute should it rotate in order to simulate Earth's gravity-that is, so the normal force on an astronaut at the outer edge would equal the astronaut's weight on Earth?

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
01:34

Problem 61

In a loop-the-loop roller coaster, show that a car moving too slowly would leave the track at an angle $\phi$ given by $\cos \phi=v^{2} / r g$ where $\phi$ is the angle made by a vertical line through the center of the circular track and a line from the center to the point where the car leaves the track.

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
02:41

Problem 62

Find an expression for the minimum frictional coefficient needed to keep a car with speed $v$ on a banked turn of radius $R$ designed for speed $v_{0}$.

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
02:43

Problem 63

An astronaut is training in an earthbound centrifuge that consists of a small chamber whirled horizontally at the end of a $5.1-\mathrm{m}-$ long shaft. The astronaut places a notebook on the vertical wall of the chamber and it stays in place. If the coefficient of static friction is $0.62,$ what's the minimum rate at which the centrifuge must be revolving?

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
04:24

Problem 64

You stand on a spring scale at the north pole and again at the equator. Which scale reading will be lower, and by what percentage will it be lower than the higher reading? Assume $g$ has the same value at pole and equator.

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
02:36

Problem 65

Driving in thick fog on a horizontal road, you spot a tractortrailer truck jackknifed across the road. To avert a collision, you could brake to a stop or swerve in a circular arc, as suggested in Fig. $5.37 .$ Which option offers the greater margin of safety? Assume that there is the same coefficient of static friction in both cases, and that you maintain constant speed if you swerve.

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
04:11

Problem 66

A block is projected up an incline at angle $\theta$. It returns to its initial position with half its initial speed. Show that the coefficient of kinetic friction is $\mu_{k}=\frac{3}{5} \tan \theta$.

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
02:14

Problem 67

A 2.1 -kg mass is connected to a spring with spring constant $k=150 \mathrm{N} / \mathrm{m}$ and unstretched length $18 \mathrm{cm} .$ The two are mounted on a frictionless air table, with the free end of the spring attached to a frictionless pivot. The mass is set into circular motion at $1.4 \mathrm{m} / \mathrm{s} .$ Find the radius of its path.

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
01:57

Problem 68

Take $\mu_{\mathrm{k}}=0.75$ in Example $5.11,$ and plot the tension force in units of the trunk's weight, as a function of the rope angle $\theta$ (that is, plot $T / m g$ versus $\theta$ ). Use your plot to determine (a) the minimum tension necessary to move the trunk and (b) the angle at which this minimum tension should be applied.

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
03:17

Problem 69

Repeat the preceding problem for an arbitrary value of $\mu_{\mathrm{k}},$ by using calculus to find the minimum force needed to move the trunk with constant speed.

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
03:52

Problem 70

Moving through a liquid, an object of mass $m$ experiences a resistive drag force proportional to its velocity, $F_{\mathrm{drag}}=-b v,$ where $b$ is a constant. (a) Find an expression for the object's speed as a function of time, when it starts from rest and falls vertically through the liquid. (b) Show that it reaches a terminal velocity $m g / b$.

Supratim Pal
Supratim Pal
Numerade Educator
04:34

Problem 71

Suppose the object in Problem 70 had an initial velocity in the horizontal direction equal to the terminal speed, $v_{x 0}=m g / b .$ Show that the horizontal distance it can go is limited to $x_{\max }=m v_{x 0} / b$ and find an expression for its trajectory ( $y$ as a function of $x$ ).

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
02:22

Problem 72

A block is launched with speed $v_{0}$ up a slope making an angle
$\theta$ with the horizontal; the coefficient of kinetic friction is $\mu_{\mathrm{k}}$
(a) Find an expression for the distance $d$ the block travels along the slope. (b) Use calculus to determine the angle that minimizes $d$.

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
07:32

Problem 73

A florist asks you to make a window display with two hanging pots as shown in Fig. $5.38 .$ The florist is adamant that the strings be as invisible as possible, so you decide to use fishing line but want to use the thinnest line you can. Will fishing line that can withstand $100 \mathrm{N}$ of tension work?
CAN'T COPY THE FIGURE

Prabhat Tyagi
Prabhat Tyagi
Numerade Educator
01:50

Problem 74

You're at the state fair. A sideshow barker claims that the star of the show can throw a 7.3 -kg Olympic-style hammer "faster than a speeding bullet." You recall that bullets travel at several hundreds of meters per second. The burly hammer thrower whirls the hammer in a circle that you estimate to be 2.4 m in diameter. You guess the chain holding the hammer makes an angle of $10^{\circ}$ with the horizontal. When the hammer flies off, is it really moving faster than a bullet?

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
01:04

Problem 75

One of the limiting factors in high-performance aircraft is the acceleration to which the pilot can be subjected without blacking out; it's measured in "gees," or multiples of the gravitational acceleration. The $\mathrm{F}-22$ Raptor fighter can achieve Mach 1.8(1.8 times the speed of sound, which is about $340 \mathrm{m} / \mathrm{s}$ ). Suppose a pilot dives in a circle and pulls up. If the pilot can't exceed $6 g$, what's the tightest circle (smallest radius) in which the plane can turn?

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
02:26

Problem 76

Figure 5.39 shows an apparatus used to verify Newton's second law. A "pulling mass" $m_{1}$ hangs vertically from a string of negligible mass that passes over a pulley, also of negligible mass and with nearly frictionless bearings. The other end of the string is attached to a glider of mass $m_{2}$ riding on an essentially frictionless, horizontal air track. Both $m_{1}$ and $m_{2}$ may be varied by placing additional masses on the pulling mass and glider. The experiment consists of starting the glider from rest and letting the pulling mass accelerate it down the track. Three photogates are used to time the glider over two distance intervals, and an experimental value for its acceleration is determined from these data, using constant-acceleration equations from Chapter $2 .$ The table in the next column lists the measured acceleration for a number of mass combinations. (a) Determine a quantity that, when plotted on the horizontal axis of a graph, should result in a straight line of slope $g$ when acceleration is plotted on the vertical axis. (b) Make your plot, fit a line to the plotted data, and report the experimentally determined value of $g$.
CAN'T COPY THE FIGURE
$$\begin{array}{ccc}
\hline m_{1}(\mathrm{g}) & m_{2}(\mathrm{g}) & a\left(\mathrm{m} / \mathrm{s}^{2}\right) \\
\hline 10.0 & 170 & 0.521 \\
10.0 & 270 & 0.376 \\
10.0 & 370 & 0.274 \\
20.0 & 170 & 1.06 \\
20.0 & 270 & 0.652 \\
20.0 & 370 & 0.534 \\
\hline
\end{array}$$

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
00:57

Problem 77

A spiral is an ice-skating position in which the skater glides on one foot with the other foot
held above hip level. It's a required element in women's singles figure skating competition and is related to the arabesque performed in ballet. Figure 5.40 shows skater Sarah Hughes executing a spiral during her gold-medal performance at the Winter Olympics in Salt Lake City.
From the photo, you can conclude that the skater is
a. executing a turn to her left.
b. executing a turn to her right.
c. moving in a straight line out of the page.

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
00:58

Problem 78

A spiral is an ice-skating position in which the skater glides on one foot with the other foot
held above hip level. It's a required element in women's singles figure skating competition and is related to the arabesque performed in ballet. Figure 5.40 shows skater Sarah Hughes executing a spiral during her gold-medal performance at the Winter Olympics in Salt Lake City.
The net force on the skater
a. points to her left.
b. points to her right.
c. is zero.

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
01:09

Problem 79

A spiral is an ice-skating position in which the skater glides on one foot with the other foot
held above hip level. It's a required element in women's singles figure skating competition and is related to the arabesque performed in ballet. Figure 5.40 shows skater Sarah Hughes executing a spiral during her gold-medal performance at the Winter Olympics in Salt Lake City.
If the skater were to execute the same maneuver but at higher speed, the tilt evident in the photo would be
a. less.
b. greater.
c. unchanged.

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
01:12

Problem 80

A spiral is an ice-skating position in which the skater glides on one foot with the other foot
held above hip level. It's a required element in women's singles figure skating competition and is related to the arabesque performed in ballet. Figure 5.40 shows skater Sarah Hughes executing a spiral during her gold-medal performance at the Winter Olympics in Salt Lake City.
The tilt angle $\theta$ that the skater's body makes with the vertical is given approximately by $\theta=\tan ^{-1}(0.5) .$ From this you can conclude that the skater's centripetal acceleration has approximate magnitude
a. 0
b. $0.5 \mathrm{m} / \mathrm{s}^{2}$
c. $5 \mathrm{m} / \mathrm{s}^{2}$
d. can't be determined without knowing the skater's speed

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator