College Physics: A Strategic Approach Volume 1

Randall D. Knight, Brian Jones, Stuart Field

Chapter 13

Fluids - all with Video Answers

Educators

Chapter Questions

Problem 1

A typical timber wolf has a mass of $40 \mathrm{~kg}$, a typical jackrabbit a mass of $2.5 \mathrm{~kg}$. Given the scaling law presented in the passage, we'd expect the specific metabolic rate of the jackrabbit to be higher by a factor of
A. 2
B. 4
C. 8
D. 16

Prabhu Ramji

Prabhu Ramji

Numerade Educator

Problem 2

A typical timber wolf has a mass of $40 \mathrm{~kg}$, a typical jackrabbit a mass of $2.5 \mathrm{~kg}$. Given the scaling law presented in the passage, we'd expect the wolf to use than a jackrabbit in the course of a day.
A. 2
B. 4
C. 8
D. 16

Prabhu Ramji

Numerade Educator

Problem 3

Given the data of the graph, approximately how much energy, in Calories, would a $200 \mathrm{~g}$ rat use during the course of a day?
A. 10
B. 20
C. 100
D. 200

Prabhu Ramji

Numerade Educator

Problem 4

All other things being equal, species that inhabit cold climates tend to be larger than related species that inhabit hot climates. For instance, the Alaskan hare is the largest North American hare, with a typical mass of $5.0 \mathrm{~kg},$ double that of a jackrabbit. A likely explanation is that A. Larger animals have more blood flow, allowing for better thermoregulation.
B. Larger animals need less food to survive than smaller animals.
C. Larger animals have larger blood volumes than smaller animals.
D. Larger animals lose heat less quickly than smaller animals.

Prabhu Ramji

Numerade Educator

Problem 5

The passage proposes that there are quantitative "laws" of biology that have their basis in physical principles, using the scaling of specific metabolic rate with body mass as an example. Which of the following regularities among animals might also be an example of such a "law"?
A. As a group, birds have better color vision than mammals.
B. Reptiles have a much lower specific metabolic rate than mammals.
C. Predators tend to have very good binocular vision; prey animals tend to be able to see over a very wide angle.
D. Jump height varies very little among animals. Nearly all animals, ranging in size from a flea to a horse, have a maximum vertical leap that is quite similar.

Prabhu Ramji

Numerade Educator

Problem 6

A $68 \mathrm{~kg}$ cyclist is pedaling down the road at $15 \mathrm{~km} / \mathrm{h}$, using a total metabolic power of $480 \mathrm{~W}$. A certain fraction of this energy is used to move the bicycle forward, but the balance ends up as thermal energy in his body, which he must get rid of to keep cool. On a very warm day, conduction, convection, and radiation transfer little energy, and so he does this by perspiring, with the evaporation of water taking away the excess thermal energy.
If the cyclist reaches his $15 \mathrm{~km} / \mathrm{h}$ cruising speed by rolling down a hill, what is the approximate height of the hill?
A. $22 \mathrm{~m}$
B. $11 \mathrm{~m}$
C. $2 \mathrm{~m}$
D. $1 \mathrm{~m}$

Eric Mockensturm

Eric Mockensturm

Numerade Educator

Problem 7

A $68 \mathrm{~kg}$ cyclist is pedaling down the road at $15 \mathrm{~km} / \mathrm{h}$, using a total metabolic power of $480 \mathrm{~W}$. A certain fraction of this energy is used to move the bicycle forward, but the balance ends up as thermal energy in his body, which he must get rid of to keep cool. On a very warm day, conduction, convection, and radiation transfer little energy, and so he does this by perspiring, with the evaporation of water taking away the excess thermal energy.
As he cycles at a constant speed on level ground, at what rate is chemical energy being converted to thermal energy in his body, assuming a typical efficiency of $25 \%$ for the conversion of chemical energy to the mechanical energy of motion?
A. $480 \mathrm{~W}$
B. $360 \mathrm{~W}$
$\mathrm{C}_{4} 240 \mathrm{~W}$
D. 120 W

Eric Mockensturm

Eric Mockensturm

Numerade Educator

Problem 8

A $68 \mathrm{~kg}$ cyclist is pedaling down the road at $15 \mathrm{~km} / \mathrm{h}$, using a total metabolic power of $480 \mathrm{~W}$. A certain fraction of this energy is used to move the bicycle forward, but the balance ends up as thermal energy in his body, which he must get rid of to keep cool. On a very warm day, conduction, convection, and radiation transfer little energy, and so he does this by perspiring, with the evaporation of water taking away the excess thermal energy.
To keep from overheating, the cyclist must get rid of the excess thermal energy generated in his body. If he cycles at this rate for 2 hours, how many liters of water must he perspire, to the nearest 0.1 liter?
A. $0.4 \mathrm{~L}$
B. $0.9 \mathrm{~L}$
C. $1.1 \mathrm{~L}$
D. $1.4 \mathrm{~L}$

David Zywotko

Numerade Educator

Problem 9

A $68 \mathrm{~kg}$ cyclist is pedaling down the road at $15 \mathrm{~km} / \mathrm{h}$, using a total metabolic power of $480 \mathrm{~W}$. A certain fraction of this energy is used to move the bicycle forward, but the balance ends up as thermal energy in his body, which he must get rid of to keep cool. On a very warm day, conduction, convection, and radiation transfer little energy, and so he does this by perspiring, with the evaporation of water taking away the excess thermal energy.
Being able to exhaust this thermal energy is very important. If he isn't able to get rid of any of the excess heat, by how much will the temperature of his body increase in 10 minutes of riding, to the nearest $0.1^{\circ} \mathrm{C}$ ?
A. $0.3^{\circ} \mathrm{C}$
B. $0.6^{\circ} \mathrm{C}$
C. $0.9^{\circ} \mathrm{C}$
D. $1.2^{\circ} \mathrm{C}$

David Zywotko

Numerade Educator

Problem 10

A balloon launched from sea level has a volume of approximately $4 \mathrm{~m}^{3}$. What is the approximate buoyant force on the balloon?
A. $50 \mathrm{~N}$
B. $40 \mathrm{~N}$
C. $20 \mathrm{~N}$
D. $10 \mathrm{~N}$

Prabhu Ramji

Numerade Educator

Problem 11

A balloon launched from sea level with a volume of $4 \mathrm{~m}^{3}$ will have a volume of about $12 \mathrm{~m}^{3}$ on reaching an altitude of 10 $\mathrm{km}$. What is the approximate buoyant force now?
A. $50 \mathrm{~N}$
B. $40 \mathrm{~N}$
C. $20 \mathrm{~N}$
D. $10 \mathrm{~N}$

Prabhu Ramji

Numerade Educator

Problem 12

The balloon expands as it rises, keeping the pressures inside and outside the balloon approximately equal. If the balloon rises slowly, heat transfers will keep the temperature inside the same as the outside air temperature. A balloon with a volume of $4.0 \mathrm{~m}^{3}$ is launched at sea level. where the atmospheric pressure is $100 \mathrm{kPa}$ and the temperature is $15^{\circ} \mathrm{C}$. It then rises slowly to a height of $5500 \mathrm{~m},$ where the pressure is $50 \mathrm{kPa}$ and the temperature is $-20^{\circ} \mathrm{C}$. What is the volume of the balloon at this altitude?
A. $5.0 \mathrm{~m}^{3}$
B. $6.0 \mathrm{~m}^{3}$
$\mathrm{C} .7 .0 \mathrm{~m}^{3}$
D. $8.0 \mathrm{~m}^{3}$

Prabhu Ramji

Numerade Educator

Problem 13

If the balloon rises quickly, so that no heat transfer is possible, the temperature inside the balloon will drop as the gas expands. If a $4.0 \mathrm{~m}^{3}$ balloon is launched at a pressure of $100 \mathrm{kPa}$ and rapidly rises to a point where the pressure is $50 \mathrm{kPa}$, the volume of the balloon will be
A. Greater than $8.0 \mathrm{~m}^{3}$
B. $8.0 \mathrm{~m}^{3}$
C. Less than $8.0 \mathrm{~m}^{3}$

Prabhu Ramji

Numerade Educator

Problem 14

At the end of the flight, the radiosonde is dropped and falls to earth by parachute. Suppose the parachute achieves its terminal speed at a height of $30 \mathrm{~km}$. As it descends into the atmosphere, how does the terminal speed change?
A. It increases.
B. It stays the same.
C. It decreases.

Prabhu Ramji

Numerade Educator

Problem 15

A balloon is launched at sea level, where the air pressure is $100 \mathrm{kPa}$. The helium has a volume of $1000 \mathrm{~m}^{3}$ at this altitude. What is the volume of the helium when the balloon has risen to a height where the atmospheric pressure is $33 \mathrm{kPa}$ ?
A. $330 \mathrm{~m}^{3}$
B. $500 \mathrm{~m}^{3}$
C. $1000 \mathrm{~m}^{3}$
D. $3000 \mathrm{~m}^{3}$

Prabhu Ramji

Numerade Educator

Problem 16

A balloon is launched at sea level, where the air pressure is $100 \mathrm{kPa}$. The density in the hot-air chamber is $1.0 \mathrm{~kg} / \mathrm{m}^{3}$. What is the density of the air when the balloon has risen to a height where the atmospheric pressure is $33 \mathrm{kPa} ?$
A. $3.0 \mathrm{~kg} / \mathrm{m}^{3}$
B. $1.0 \mathrm{~kg} / \mathrm{m}^{3}$
C. $0.66 \mathrm{~kg} / \mathrm{m}^{3}$
D. $0.33 \mathrm{~kg} / \mathrm{m}^{3}$

Prabhu Ramji

Numerade Educator

Problem 17

A balloon is at a height of $5.0 \mathrm{~km}$ and is descending at a constant rate. The buoyancy force is directed force is directed
A. Up, up
B. Up, down
C. Down, up
D. Down, down

Prabhu Ramji

Numerade Educator

Problem 18

When you exhale, all of the air in your lungs must exit through the trachea. If you exhale through your nose, this air subsequently leaves through your nostrils. The area of your nostrils is less than that of your trachea. How does the speed of the air in the trachea compare to that in the nostrils?

Prabhu Ramji

Numerade Educator

Problem 19

Sneezing requires an increase in pressure of the air in the lungs; a typical sneeze might result in an extra pressure of $7.0 \mathrm{kPa}$. Estimate how much force this exerts on the diaphragm, the large muscle at the bottom of the ribcage.

Khoobchandra Agrawal

Khoobchandra Agrawal

Numerade Educator

Problem 20

A $20 \mathrm{~kg}$ block of aluminum sits on the bottom of a tank of water. How much force does the block exert on the bottom of the tank? $?$

Prabhu Ramji

Numerade Educator

Problem 21

We ve seen that fish can control their buoyancy through the use of a swim bladder, a gas-filled organ inside the body. You can assume that the gas pressure inside the swim bladder is roughly equal to the external water pressure. A fish swimming at a particular depth adjusts the volume of its swim bladder to give it neutral buoyancy. If the fish swims upward or downward, the changing water pressure causes the bladder to expand or contract. Consequently, the fish must adjust the quantity of gas to restore the original volume and thus reestablish neutral buoyancy. Consider a large, $7.0 \mathrm{~kg}$ striped bass with a volume of $7.0 \mathrm{~L}$. When neutrally buoyant, $7.0 \%$ of the fish's volume is taken up by the swim bladder. Assume a body temperature of $15^{\circ} \mathrm{C}$.
a. How many moles of air are in the swim bladder when the fish is at a depth of $80 \mathrm{ft}$ ?
b. What will the volume of the swim bladder be if the fish ascends to a $50 \mathrm{ft}$ depth without changing the quantity of gas?
c. To return the swim bladder to its original size, how many moles of gas must be added?

Khoobchandra Agrawal

Khoobchandra Agrawal

Numerade Educator