Midterm Examination 2 Solutions

Problem 1:

Suppose a huge alien spaceship were to visit us and remove half the molecules from the earth's atmosphere. The air pressure at sea level would then be approximately

(A) 12.5% of its original value. [3.5% picked]
(B) unchanged. [18.1% picked]
(C) 50% of its original value. [66.8% picked]
(D) 25% of its original value. [10.2% picked]

Answer: (C) 50% of its original value. [66.8% picked]

Why: Movie Video Discussion

Problem 2:

When water flows around a bend in a garden hose, the water pressure

(A) increases near the inside of the curve and decreases near the outside of the curve. [23.5% picked]
(B) decreases near the inside of the curve and increases near the outside of the curve. [75.2% picked]
(C) increases near the inside of the curve and increases near the outside of the curve. [0.9% picked]
(D) decreases near the inside of the curve and decreases near the outside of the curve. [0.4% picked]

Answer: (B) decreases near the inside of the curve and increases near the outside of the curve. [75.2% picked]

Why: Movie Video Discussion

Problem 3:

You are trying to set the world's record for drinking water through the tallest drinking straw. What could you do to have the best chance of setting this record?

(A) Use the widest drinking straw you can fit in your mouth. [19.0% picked]
(B) Go to the lowest altitude available, preferably sea level or below. [38.1% picked]
(C) Use the narrowest drinking straw you can find. [16.8% picked]
(D) Go to the highest altitude available, preferably at the top of a tall mountain. [26.1% picked]

Answer: (B) Go to the lowest altitude available, preferably sea level or below. [38.1% picked]

Why: Movie Video Discussion

Problem 4:

When you pour milk from a pitcher into a bowl, the flow is likely to become turbulent. When you pour honey from a jar into a bowl, however, the flow is likely to remain laminar. Compared to milk, honey is more likely to exhibit laminar flow because honey's larger

(A) weight tends to keep the flow orderly. [0.4% picked]
(B) viscosity tends to keep the flow orderly. [94.2% picked]
(C) density tends to keep the flow orderly. [4.9% picked]
(D) inertia tends to keep the flow orderly. [0.4% picked]

Answer: (B) viscosity tends to keep the flow orderly. [94.2% picked]

Why: Movie Video Discussion

Problem 5:

You are holding an umbrella over your head on a windy day. As the wind blows across the dome-shaped top of the umbrella, the airstream is curving toward the umbrella's surface. The air pressure just above the peak of the umbrella is

(A) less than atmospheric pressure. [70.4% picked]
(B) equal to atmospheric pressure. [5.8% picked]
(C) more than atmospheric pressure. [22.6% picked]
(D) less than zero pressure. [0.9% picked]

Answer: (A) less than atmospheric pressure. [70.4% picked]

Why: Movie Video Discussion

Problem 6:

You are standing 10 feet north of a campfire in a level, open field. Despite the cool air all around you, you feel warmed by the fire. Heat is flowing from the fire to you

(A) mostly via thermal radiation. [73.9% picked]
(B) equally via all three heat transfer mechanism. [6.6% picked]
(C) mostly via thermal convection. [16.4% picked]
(D) mostly via thermal conduction. [3.1% picked]

Answer: (A) mostly via thermal radiation. [73.9% picked]

Why: Movie Video Discussion

Problem 7:

You are drying your hair and you have put a diffuser (an anti-nozzle) on the end of the dryer, so that it doesn't blow your naturally curly hair straight. As fast-moving air from the dryer flows through the diffuser, that air slows down and the air's

(A) particle density decreases. [2.7% picked]
(B) momentum increases. [0.0% picked]
(C) pressure increases. [92.5% picked]
(D) density decreases. [4.9% picked]

Answer: (C) pressure increases. [92.5% picked]

Why: Movie Video Discussion

Problem 8:

When a rocket leaves earth's atmosphere, there is no longer any air near it. Is the rocket still able to obtain forward thrust and, if so, what is pushing it forward?

(A) Yes, earth's atmosphere still pushes it forward. [3.1% picked]
(B) No, it cannot obtain forward thrust when there is no nearby air to push against. [6.2% picked]
(C) Yes, the earth pushes it forward. [0.9% picked]
(D) Yes, its exhaust gases push it forward. [89.4% picked]

Answer: (D) Yes, its exhaust gases push it forward. [89.4% picked]

Why: Movie Video Discussion

Problem 9:

You are a pole-vaulter and, having just cleared the bar at your personal best height, you begin to fall toward the thick foam rubber pad far below. When during your descent do you first stop accelerating downward?

(A) When you pass through equilibrium in the pad for the first time. [90.3% picked]
(B) When you reach your lowest point on the pad at the middle of your first bounce. [6.2% picked]
(C) When you touch the pad for the first time. [3.1% picked]
(D) Just before you touch the pad for the first time. [0.4% picked]

Answer: (A) When you pass through equilibrium in the pad for the first time. [90.3% picked]

Why: Movie Video Discussion

Problem 10:

As a soccer ball travels from the kicker to the goal, air approaches the front of the ball and they interact. The ball loses much of its forward momentum during its flight because

(A) the air on the sides of the ball is higher than atmospheric pressure and it squeezes the ball so that the ball slows down. [4.4% picked]
(B) the air on the sides of the ball is lower than atmospheric pressure and it sucks the ball so that the ball slows down. [15.5% picked]
(C) the air at the front of the ball is higher than atmospheric pressure while the air behind the ball is approximately atmospheric pressure. [71.7% picked]
(D) the air at the front of the ball is lower than atmospheric pressure while the air behind the ball is higher than atmospheric pressure. [7.5% picked]

Answer: (C) the air at the front of the ball is higher than atmospheric pressure while the air behind the ball is approximately atmospheric pressure. [71.7% picked]

Why: Movie Video Discussion

Problem 11:

When you try to balance a pencil on its sharpened point, it invariably tips over. That's because the upright pencil

(A) cannot be motionless. [0.9% picked]
(B) has an unstable equilibrium and it accelerates away from that equilibrium after the slightest disturbance. [95.6% picked]
(C) has no equilibrium and is always accelerating. [2.2% picked]
(D) cannot have zero angular velocity. [0.9% picked]

Answer: (B) has an unstable equilibrium and it accelerates away from that equilibrium after the slightest disturbance. [95.6% picked]

Why: Movie Video Discussion

Problem 12:

Two toy cars roll off a level table side-by-side at the same time and in the same direction. The cars soon hit the level floor below the table. The orange car weighs twice as much as the green car, but both cars were traveling at the same horizontal speed when they left the table. In this situation,

(A) the two cars hit the floor at approximately the same time and the same distance from the table. [69.9% picked]
(B) the orange car hits the floor much sooner than the green car, but the green car hits considerably farther from the table than the orange car. [1.8% picked]
(C) the two cars hit the floor at approximately the same time, but the green car hits considerably farther from the table than the orange car. [27.4% picked]
(D) the green car hits the floor much sooner than the orange car, but the green car hits considerably farther from the table than the orange car. [0.9% picked]

Answer: (A) the two cars hit the floor at approximately the same time and the same distance from the table. [69.9% picked]

Why: Movie Video Discussion

Problem 13:

You want to help a seriously ill person, but the door to their room is locked. To have the best chance of breaking the door open, you run toward the door (to accumulate forward momentum) and then hit the door with your

(A) hard shoulder so that you quickly come to a complete stop. [41.2% picked]
(B) soft derriere so that you slowly come to a complete stop. [1.3% picked]
(C) entire body so that you maximize the contact area between you and the door. [7.1% picked]
(D) hard feet and jump strongly so that you end up moving backward at the same speed you had before hitting the door. [50.4% picked]

Answer: (D) hard feet and jump strongly so that you end up moving backward at the same speed you had before hitting the door. [50.4% picked]

Why: Movie Video Discussion

Problem 14:

An airplane is cruising horizontally at 30,000 feet and is traveling at constant velocity. The overall force that airplane exerts on the air points

(A) straight backward (toward the rear of the plane). [7.1% picked]
(B) downward and forward (toward the front of the plane). [14.2% picked]
(C) downward and backward (toward the rear of the plane). [11.5% picked]
(D) straight downward. [65.9% picked]

Answer: (D) straight downward. [65.9% picked]

Why: Movie Video Discussion

Problem 15:

If the airflow passing over the top of an airplane wing suddenly breaks away from the surface of the wing and forms a turbulent wake, the airplane will experience a rise in

(A) viscous drag and an increase in lift. [7.5% picked]
(B) viscous drag, but little change in lift. [10.6% picked]
(C) pressure drag, but little change in lift. [24.8% picked]
(D) pressure drag and a decrease in lift. [57.1% picked]

Answer: (D) pressure drag and a decrease in lift. [57.1% picked]

Why: Movie Video Discussion

Problem 16:

You are designing a chair for a museum. While your chair will be a work of art, it must also be practical and it mustn't tip over easily. To ensure that it stays upright, you design it so that its

(A) center of gravity always descends if you tip it. [35.4% picked]
(B) center of gravity always rises if you tip it. [62.8% picked]
(C) angular velocity always remains constant if you tip it. [1.3% picked]
(D) velocity always remains constant if you tip it. [0.4% picked]

Answer: (B) center of gravity always rises if you tip it. [62.8% picked]

Why: Movie Video Discussion

Problem 17:

You are working in a pizza parlor. You toss a spinning disk of pizza dough into the air. As the dough stretches outward and the flying disk becomes wider, what happens to the disk's angular velocity?

(A) It remains constant because no torque acts on the disk. [4.0% picked]
(B) It increases. [14.2% picked]
(C) It remains constant because angular velocity is conserved. [2.2% picked]
(D) It decreases. [79.6% picked]

Answer: (D) It decreases. [79.6% picked]

Why: Movie Video Discussion

Problem 18:

You hold an ordinary helium-filled rubber balloon motionless in a small room filled with helium gas and then release the balloon. That balloon

(A) descends to the floor. [64.2% picked]
(B) rises to the ceiling. [9.7% picked]
(C) hovers at its original height. [21.7% picked]
(D) moves rhythmically up and down about its original height. [4.4% picked]

Answer: (A) descends to the floor. [64.2% picked]

Why: Movie Video Discussion

Problem 19:

The chemical bond that causes two oxygen atoms to cling together as an oxygen molecules is

(A) a deficit of energy—the work needed to separate those two atoms from one another. [43.4% picked]
(B) a myth; the two atoms only think that they are bound to one another. [2.2% picked]
(C) a repulsive force that the two atoms exert on one another when they are at their equilibrium separation. [2.7% picked]
(D) an attractive force that the two atoms exert on one another when they are at their equilibrium separation. [51.8% picked]

Answer: (A) a deficit of energy—the work needed to separate those two atoms from one another. [43.4% picked]

Why: Movie Video Discussion

Problem 20:

You leave the bathroom window open on a cold day and find that your cloth towel, the metal towel rack, and the ceramic tile wall are all at 50 °F. When those three objects are touching one another, heat

(A) flows from the metal rack to both the cloth towel and the ceramic tile wall. [19.0% picked]
(B) flows from the cloth towel to both the metal rack and the ceramic tile wall. [4.0% picked]
(C) flows from the ceramic tile wall to both the cloth towel and metal rack. [4.0% picked]
(D) does not flow among them. [73.0% picked]

Answer: (D) does not flow between them. [73.0% picked]

Why: Movie Video Discussion

Problem 21:

Firefighters are battling a fire on the 10th floor of an apartment building. When they stand on the ground, their fire hose can only shoot the water steadily up to the 8th floor. So they carry the nozzle end of the same fire hose to the top of a 2-story-tall ladder and again direct its spray upward. Now the fire hose can shoot the water steadily up to the

(A) 9th floor. [0.9% picked]
(B) 10th floor. [6.6% picked]
(C) 6th floor. [0.0% picked]
(D) 8th floor. [92.5% picked]

Answer: (D) 8th floor. [92.5% picked]

Why: Movie Video Discussion

Problem 22:

If a skyscraper supplied water to all of its floors through a single vertical pipe,

(A) the water pressure would be much greater at the upper floors than at the lower floors. [3.1% picked]
(B) the water pressure would be much greater at the lower floors than at the upper floors. [91.6% picked]
(C) the total energy per drop of water would be much greater at the lower floors than at the upper floors. [2.7% picked]
(D) the total energy per drop of water would be much greater at the upper floors than at the lower floors. [2.7% picked]

Answer: (B) the water pressure would be much greater at the lower floors than at the upper floors. [91.6% picked]

Why: Movie Video Discussion

Problem 23:

A rocket designed to put a satellite in orbit around the earth has two main tasks. First, it must lift the satellite above earth's atmosphere to eliminate air resistance. Second, it must

(A) give the satellite such a large horizontal speed that the falling satellite arcs endlessly around the earth rather than descending to the ground. [76.5% picked]
(B) push upward on the satellite with a force that balances the satellite's downward weight so that the satellite can coast at constant velocity. [17.3% picked]
(C) give the satellite such a large sideways acceleration that the satellite's apparent weight is zero. [3.5% picked]
(D) give the satellite such a large upward vertical speed that the falling satellite cannot descend to the ground. [2.2% picked]

Answer: (A) give the satellite such a large horizontal speed that the falling satellite arcs endlessly around the earth rather than descending to the ground. [76.5% picked]

Why: Movie Video Discussion

Problem 24:

You are swinging an open can of paint around in a horizontal circle at a steady speed. Your friends watch as the can circles from north to west to south to east to north, over and over again. As the can reaches its northern position, you accidentally let go of the can and the paint splatters one of your friends. In which direction did the paint travel after you released it?

(A) Toward the west. [49.1% picked]
(B) Toward the north. [23.5% picked]
(C) Toward the northwest. [17.3% picked]
(D) Toward the southwest. [9.7% picked]

Answer: (A) Toward the west. [49.1% picked]

Why: Movie Video Discussion

Problem 25:

You are riding a rollercoaster with a loop-the-loop. You have just rolled up the side of the loop and are, at this moment, exactly at the top of the loop. You and the car are upside down, yet you are pressed tightly into your seat. At this moment, you are accelerating

(A) downward at the acceleration due to gravity. [16.4% picked]
(B) downward at more than the acceleration due to gravity. [63.3% picked]
(C) upward at a rate equal in amount to the acceleration due to gravity. [13.7% picked]
(D) downward at less than the acceleration due to gravity. [6.6% picked]

Answer: (B) downward at more than the acceleration due to gravity. [63.3% picked]

Why: Movie Video Discussion

Problem 26:

You are playing miniature golf with friends and, as part of one hole, your golf ball rolls on a series of different ramps. The ramps are all flat surfaces, but they have different steepnesses. As the ball moves onto steeper and steeper ramps, the ball's

(A) velocity remains unchanged. [1.3% picked]
(B) acceleration becomes greater. [60.6% picked]
(C) speed is smaller when it is heading up the ramp and greater when it is moving down the ramp. [28.3% picked]
(D) velocity becomes greater. [9.7% picked]

Answer: (B) acceleration becomes greater. [60.6% picked]

Why: Movie Video Discussion

Problem 27:

As water flows upward in a vertical pipe that has a uniform diameter, the water's gravitational potential energy increases,

(A) neither its pressure potential energy nor its kinetic energy change. [2.2% picked]
(B) both its pressure potential energy and its kinetic energy decrease. [17.3% picked]
(C) its pressure potential energy decreases, but its kinetic energy remains constant. [73.0% picked]
(D) its kinetic energy decreases, but its pressure potential energy remains constant. [7.1% picked]

Answer: (C) its pressure potential energy decreases, but its kinetic energy remains constant. [73.0% picked]

Why: Movie Video Discussion

Problem 28:

On a cold morning, you seal your empty plastic water bottle and thus trap the air inside it. Later in the day, the bottle and its contents are much warmer and the elastic sides of the bottle are now stretched outward. The bottle's volume has increased. Based on these changes, you can be certain that the air pressure inside the bottle has

(A) increased and the density inside the bottle has increased. [6.2% picked]
(B) increased, but the density inside the bottle has stayed the same. [4.9% picked]
(C) stayed the same, but the density inside the bottle has decreased. [2.7% picked]
(D) increased, but the density inside the bottle has decreased. [86.3% picked]

Answer: (D) increased, but the density inside the bottle has decreased. [86.3% picked]

Why: Movie Video Discussion

Problem 29:

You are at a barbeque and the bottle of hot sauce is almost empty. You put the cap on the bottle and swing it rapidly in a circle with its cap end pointing outward. The remaining sauce collects just inside the cap and you are able to extract enough to spice up your vanilla ice cream. This technique works because

(A) centrifugal force pushes the hot sauce toward the cap end of the bottle. [2.7% picked]
(B) the force of the hot sauce's momentum pushes it toward the cap end of the bottle. [1.3% picked]
(C) the bottle's rapid inward acceleration leaves the hot sauce behind so that it drifts toward the cap end of the bottle. [94.7% picked]
(D) viscous forces push the hot sauce toward the cap end of the bottle. [1.3% picked]

Answer: (C) the bottle's rapid inward acceleration leaves the hot sauce behind so that it drifts toward the cap end of the bottle. [94.7% picked]

Why: Movie Video Discussion

Problem 30:

You're at the lake and watch two children jump off a dock at the same time. They both kick equally hard during their jumps, but one child jumps mostly upward while the other child jumps mostly forward. After they leave the dock,

(A) the two children reach the water at the same moment and at the same distance from the dock. [0.0% picked]
(B) the child who jumps upward reaches the water before the child who jumps forward. [0.0% picked]
(C) the child who jumps forward reaches the water before the child who jumps upward. [93.8% picked]
(D) the two children reach the water at the same moment and but the child who jumps forward travels farther from the dock than does the other child. [6.2% picked]

Answer: (C) the child who jumps forward reaches the water before the child who jumps upward. [93.8% picked]

Why: Movie Video Discussion