Question 1

A dump truck has a loosely tied canvas over its empty bed, which is full of still air. As the truck speeds down the highway, the canvas will tend to
A) get pushed onto the load.
B) billow outward from the load.
C) smooth out in a level, horizontal plane.
D) lay limply in a jumbled pile.

Accepted Answer

As the truck speeds down the highway, the air in the truck bed will experience wind resistance and will tend to move outwards. This will cause the canvas to billow outward from the load.

Question 2

A uniform wooden plank floats in a swimming pool. The plank weighs 100 pounds, and exactly 10% of its volume is above the waterline. The maximum weight of iron which could be suspended from underneath the plank without causing the whole combination to sink to the bottom of the pool is
A) exactly 10 pounds.
B) somewhat more than 10 pounds.
C) somewhat less than 10 pounds.
D) more information is needed.

Accepted Answer

The plank displaces water equal to its own weight (100 pounds) when floating. Since only 10% of the plank is above water, it means 90% of its volume is used to displace this weight in water. If iron is added, it will increase the weight without significantly changing the volume, allowing the plank to displace more water up to its maximum buoyant capacity. Therefore, the maximum weight of iron that can be added is somewhat more than 10 pounds, as this would utilize the remaining buoyant capacity of the plank without exceeding it.

Question 3

One section of a pipe carrying water has a cross-sectional area of 16 cm²; in this section the water has flow velocity of 1.0 m/s. Another section of this pipe has a constricted cross-sectional area of 4 cm². If the flow is steady, what is the water velocity in the constricted section? A) 4.0 m/s B) 2.0 m/s C) 1.0 m/s D) 0.50 m/s E) 0.25 m/s

Accepted Answer

The principle of conservation of mass (continuity equation) for fluids states that the product of cross-sectional area and velocity is constant throughout a pipe. Therefore, if the area is reduced to a quarter (from 16 cm² to 4 cm²), the velocity must increase fourfold (from 1.0 m/s to 4.0 m/s).

Question 4

A gas originally occupies a volume of 0.5 m³ at a pressure of 100 kPa. It is slowly allowed to expand until the volume is 2.5 m³. Assuming the temperature is kept constant, the final pressure will be A) 500 kPa. B) 100 kPa. C) 50 kPa. D) 20 kPa. E) 10 kPa.

Accepted Answer

According to Boyle's Law (P1V1 = P2V2), if the temperature is constant, the pressure and volume of a gas are inversely proportional. So, P2 = (P1V1)/V2 = (100 kPa * 0.5 m³) / 2.5 m³ = 20 kPa.

Question 5

A person wearing snowshoes can walk across a blanket of freshly fallen snow without sinking far into the snow because
A) the snowshoes reduce the force of the person on the snow.
B) the large area of the snowshoe concentrates the force of the person to a point smaller than the foot.
C) snowshoes cover a larger area than a foot and so the pressure is reduced.
D) snowshoes push less dense snow out of the way so the person stands on more solid ice below.

Accepted Answer

Snowshoes cover a larger area than a foot, distributing the weight of the person over a larger surface area, which reduces the pressure on the snow and prevents the person from sinking too far into the snow.

Question 6

In U.S. customary units, air pressure is measured in pounds per square inch. In the metric system, it is measured in Pascals, and one Pascal is equal to
A) one pound per square foot.
B) one newton per square meter.
C) one newton per square centimeter.
D) one metric ton per hectare.
E) none of these.

Accepted Answer

One Pascal is defined as one newton of force per square meter of area.

Question 7

Suppose a little bubble of air has gotten into the top of a mercury barometer. If a person uses a barometer in the usual way, the reading of atmospheric pressure will be
A) correct.
B) higher than the actual value.
C) lower than the actual value.

Accepted Answer

The presence of an air bubble in the mercury column of a barometer will cause the mercury level to be lower than it should be for a given atmospheric pressure, because the bubble will take up some space at the top and prevent the mercury from rising as high as it would without the bubble. This results in a reading that is lower than the actual atmospheric pressure.

Question 8

The glass in a window is 35 inches wide and 20 inches tall, and standard atmospheric pressure is 14.7 pounds per square inch. What net force would result on the glass if the air pressure outside the house were 1% lower than the air pressure inside?
A) 103 pounds inward.
B) 103 pounds outward.
C) 10300 pounds inward.
D) 10300 pounds outward.
E) There would be no net force.

Accepted Answer

The net force is calculated by finding the difference in pressure between the inside and outside of the house and then multiplying this by the area of the glass. A 1% decrease in pressure from 14.7 psi results in an external pressure of 14.553 psi (14.7 - 0.147 = 14.553 psi). The area of the glass is 35 inches * 20 inches = 700 square inches. The pressure difference is 0.147 psi (14.7 - 14.553), so the net force is 0.147 psi * 700 square inches = 102.9 pounds, rounded to 103 pounds. Since the pressure outside is lower, the net force is outward.

Question 9

One morning you discover that a tire on your auto is in need of air. This is visible: it has flattened significantly. Significant flattening indicates low air pressure
A) only if all tires are equally flattened; otherwise it is just low atmospheric pressure.
B) because more of the tire's surface area is required to provide same amount of force.
C) and less weight.
D) and higher temperature.

Accepted Answer

When the tire flattens significantly, more of its surface area comes in contact with the ground, which means more force is required to move the vehicle. This requires more energy and puts more strain on the engine, resulting in lower fuel efficiency. Additionally, the excess friction generates heat, which can cause the tire to wear out more quickly, and in some cases, burst.

Question 10

The density of aluminum is 2700 kg/m³. An aluminum block has a mass of 2.5 kg. The buoyant force exerted on this block when it is completely submerged in water of density 1000 kg/m³ is approximately A) 0.0091 N. B) 0.93 N. C) 2.5 N. D) 9.1 N. E) 24.5 N.

Accepted Answer

First, we need to find the volume of the aluminum block:

Density = mass/volume
Volume = mass/density
Volume = 2.5 kg / 2700 kg/m^3 = 0.0009259 m^3

Next, we can use Archimedes' principle to find the buoyant force:

Buoyant force = weight of water displaced
Weight of water displaced = density of water x volume of block x gravitational acceleration
Weight of water displaced = 1000 kg/m^3 x 0.0009259 m^3 x 9.81 m/s^2
Weight of water displaced = 9.065 N

Therefore, the buoyant force exerted on the block is approximately 9.1 N (rounded to one significant figure). The answer is D.

Question 11

Imagine a steel pipe that doesn't leak from the sides and is already filled with water. Water enters at a rate of 2 kg/s but leaves at a rate of 1 kg/s. Which of the following is true?
A) The water pressure inside the tube rises as water is added.
B) The tube is narrower where the water enters than where it leaves.
C) The water flow must be laminar.
D) It is not possible for this situation to occur.

Accepted Answer

The answer of Imagine a steel pipe that doesn't leak...

Question 12

The density of ice is about 900 kg/m³, and the density of water is about 1000 kg/m³. A cubic block of ice one meter on a side floats in water. Assuming that the lowest square face of the cube is horizontal, the height of the block above the water line is A) 0.9 m. B) 0.8 m. C) 0.5 m. D) 0.2 m. E) 0.1 m.

Accepted Answer

The fraction of the ice submerged is equal to the ratio of the density of ice to the density of water (900/1000 = 0.9). Therefore, 0.1 m of the 1 m block is above the water line.

Question 13

The best shape for an automobile to have is one that is streamlined both in the front and in the back. The reason for this is
A) to avoid uneven air flows that might push the vehicle sideways.
B) to improve fuel efficiency when driving in reverse.
C) to use the viscosity of the air to help propel the automobile forward.
D) to ensure the air flow remains laminar all the way around the vehicle.

Accepted Answer

The answer of The best shape for an automobile to...

Question 14

A hydraulic jack is used to lift a load of weight 4000 N. The load-bearing cylinder has a radius of 4 cm, and the other piston has a radius of 1 cm. What force must be exerted on the smaller piston to support the load?
A) 100 N
B) 250 N
C) 1000 N
D) 4000 N
E) 16,000 N

Accepted Answer

The pressure in the liquid is the same throughout the two cylinders because they are connected. Therefore, the force exerted on the load-bearing piston is equal to the force exerted on the smaller piston. Using the formula F1/A1 = F2/A2, where F1 is the force on the load-bearing piston (4000 N), A1 is the area of the load-bearing piston (πr1^2 = π(0.04m)^2 = 0.00502 m^2), F2 is the force on the smaller piston, and A2 is the area of the smaller piston (πr2^2 = π(0.01m)^2 = 0.000314 m^2), we can solve for F2. 
F2 = F1 * (A2/A1) = 4000 N * (0.000314 m^2 / 0.00502 m^2) ≈ 250 N. 
Therefore, the force that must be exerted on the smaller piston to support the load is 250 N.

Question 15

Atmospheric pressure decreases as one moves to higher elevations because
A) the force of gravity is weaker on a mountain than at sea level.
B) it is much colder on a mountain than at sea level.
C) the air moves at higher speeds near mountains than over the oceans.
D) there is much less air above a mountain than above the oceans.

Accepted Answer

Atmospheric pressure is the weight of the air above a certain point. As one moves to higher elevations, there is less air above that point, so the weight and therefore pressure decreases.

Question 16

How does the velocity of air moving over the top of the wing of an airplane in flight compare to the velocity of air moving under the wing?
A) The velocities are the same.
B) The velocity over the wing is greater.
C) The velocity under the wing is greater.

Accepted Answer

According to the Bernoulli's principle, as the air moves over the curved top of the wing, its velocity increases and the pressure decreases. This creates a region of low pressure above the wing, which helps lift the airplane. In contrast, the air moving under the wing moves slower and experiences higher pressure. Therefore, the velocity of the air over the wing is greater than the velocity of the air under the wing.

Question 17

A block that has a density of 900 kg/m³ is placed in water (density 1000 kg/m³). The block will A) sink to the bottom. B) sink until it is almost, but not entirely, submerged. C) sink until it is entirely submerged and then remain in place just below the surface. D) sink just a little bit with most of the block above the water. E) rest on the water with none of the block submerged.

Accepted Answer

The block will sink until it is almost, but not entirely, submerged because its density is less than that of water, allowing it to float, but since its density is close to that of water, a significant portion will be submerged to displace enough water to support its weight.

Question 18

Some people say that, based on the arrangement of its molecules, glass should be considered a liquid. If we think of glass as a liquid, in which of these properties is it most unlike other common liquids?
A) Weight
B) Density
C) Transparency
D) Viscosity

Accepted Answer

If glass is considered a liquid, its viscosity is the most unlike other common liquids. This is because the viscosity of glass is much higher than other liquids, meaning that it resists flow more strongly. Typically, liquids flow more easily than solids, but the high viscosity of glass means that it behaves more like a solid in this respect. The weight, density, and transparency of glass are all similar to those of other common liquids.

Question 19

According to Bernoulli's equation, the pressure in a fluid will tend to decrease if its velocity increases. Assuming that a wind speed of 1 m/s causes a pressure drop of 0.645 Pa, what pressure drop is predicted by Bernoulli's equation for a wind speed of 5 m/s?
A) 1.29 Pa
B) 1.94 Pa
C) 3.325 Pa
D) 16.125 Pa

Accepted Answer

Bernoulli's equation implies that the pressure drop is proportional to the square of the velocity. Given that a wind speed of 1 m/s causes a pressure drop of 0.645 Pa, a wind speed of 5 m/s (which is 5 times greater) would cause a pressure drop of $0.645 \times 5^2 = 0.645 \times 25 = 16.125$ Pa.

Question 20

Two cylindrical pipes both carry an ideal fluid (zero viscosity) in laminar flow. Pipe A has radius R_A = 8 cm and flow velocity v_A = 2 cm/s. Pipe B has radius R_B = 4 cm and flow velocity v_B = 4 cm/s. Compared to the rate of flow in pipe A, that in pipe B is A) the same. B) half as large. C) twice as large. D) It depends on the length of the pipe.

Accepted Answer

The rate of flow in a cylindrical pipe is given by the equation Q = πr^2v, where Q is the volume flow rate, r is the radius of the pipe, and v is the flow velocity. Since pipe B has a smaller radius than pipe A, but a larger flow velocity, the volume flow rate in pipe B is half as large as pipe A. Thus, the answer is B. The length of the pipe does not affect the answer, as long as laminar flow is maintained throughout the length of the pipe.

Quiz 9: The Behavior of Fluids

A dump truck has a loosely tied canvas over its empty bed, which is full of still air. As the truck speeds down the highway, the canvas will tend to

A uniform wooden plank floats in a swimming pool. The plank weighs 100 pounds, and exactly 10% of its volume is above the waterline. The maximum weight of iron which could be suspended from underneath the plank without causing the whole combination to sink to the bottom of the pool is

One section of a pipe carrying water has a cross-sectional area of 16 cm²; in this section the water has flow velocity of 1.0 m/s. Another section of this pipe has a constricted cross-sectional area of 4 cm². If the flow is steady, what is the water velocity in the constricted section?

A gas originally occupies a volume of 0.5 m³ at a pressure of 100 kPa. It is slowly allowed to expand until the volume is 2.5 m³. Assuming the temperature is kept constant, the final pressure will be

A person wearing snowshoes can walk across a blanket of freshly fallen snow without sinking far into the snow because

In U.S. customary units, air pressure is measured in pounds per square inch. In the metric system, it is measured in Pascals, and one Pascal is equal to

Suppose a little bubble of air has gotten into the top of a mercury barometer. If a person uses a barometer in the usual way, the reading of atmospheric pressure will be

The glass in a window is 35 inches wide and 20 inches tall, and standard atmospheric pressure is 14.7 pounds per square inch. What net force would result on the glass if the air pressure outside the house were 1% lower than the air pressure inside?

One morning you discover that a tire on your auto is in need of air. This is visible: it has flattened significantly. Significant flattening indicates low air pressure

The density of aluminum is 2700 kg/m³. An aluminum block has a mass of 2.5 kg. The buoyant force exerted on this block when it is completely submerged in water of density 1000 kg/m³ is approximately

Imagine a steel pipe that doesn't leak from the sides and is already filled with water. Water enters at a rate of 2 kg/s but leaves at a rate of 1 kg/s. Which of the following is true?

The density of ice is about 900 kg/m³, and the density of water is about 1000 kg/m³. A cubic block of ice one meter on a side floats in water. Assuming that the lowest square face of the cube is horizontal, the height of the block above the water line is

The best shape for an automobile to have is one that is streamlined both in the front and in the back. The reason for this is

A hydraulic jack is used to lift a load of weight 4000 N. The load-bearing cylinder has a radius of 4 cm, and the other piston has a radius of 1 cm. What force must be exerted on the smaller piston to support the load?

Atmospheric pressure decreases as one moves to higher elevations because

How does the velocity of air moving over the top of the wing of an airplane in flight compare to the velocity of air moving under the wing?

A block that has a density of 900 kg/m³ is placed in water (density 1000 kg/m³) . The block will

Some people say that, based on the arrangement of its molecules, glass should be considered a liquid. If we think of glass as a liquid, in which of these properties is it most unlike other common liquids?

According to Bernoulli's equation, the pressure in a fluid will tend to decrease if its velocity increases. Assuming that a wind speed of 1 m/s causes a pressure drop of 0.645 Pa, what pressure drop is predicted by Bernoulli's equation for a wind speed of 5 m/s?

Two cylindrical pipes both carry an ideal fluid (zero viscosity) in laminar flow. Pipe A has radius R_A = 8 cm and flow velocity v_A = 2 cm/s. Pipe B has radius R_B = 4 cm and flow velocity v_B = 4 cm/s. Compared to the rate of flow in pipe A, that in pipe B is