PHYS 1060 Spring 2010 - Midterm 2 - Solutions

PHYS 1060 Midterm Exam 1, Spring 2010 - Solutions

Problem 1:

When a modern car crashes into a tree and comes to an abrupt stop, the driver's face and chest collide with an air bag rather than with the steering wheel. The driver's chances of serious injury are reduced by hitting the air bag rather than the steering wheel because the driver transfers

(A) the same amount of momentum to the air bag as he would to the steering wheel, but he does so with a larger force over a shorter period of time. [2.5% picked]

(B) the same amount of momentum to the air bag as he would to the steering wheel, but he does so with a smaller force over a longer period of time. [95.5% picked]

(C) more momentum to the air bag than he would to the steering. [0.8% picked]

(D) less momentum to the air bag than he would to the steering. [1.2% picked]

Answer: (B) the same amount of momentum to the air bag as he would to the steering wheel, but he does so with a smaller force over a longer period of time. [95.5% picked]

Why: Video Discussion

Problem 2:

A van de Graaff static generator has a huge amount of electric charge on its ball-shape top. If you move your hand slowly toward the ball, a spark will occur when your hand is about 12 inches from the ball. If you hold a sharp metal needle in your hand, aimed at the ball, and move your hand slowly toward the ball,

(A) a spark will occur when your hand is much more than 12 inches from the ball. [9.4% picked]

(B) a spark will occur when your hand is much less than 12 inches from the ball. [5.3% picked]

(C) a spark will occur when your hand is about 12 inches from the ball. [1.2% picked]

(D) no spark will occur. [84.0% picked]

Answer: (D) no spark will occur. [84.0% picked]

Why: Video Discussion

Problem 3:

Two hikers carry identical backpacks from a nature center to the top of a nearby mountain. One hiker takes the short, steep trail to the top and arrives first. The second hiker takes the long, gradual trail to the top and arrives second. Which hiker did the most work on his backpack?

(A) The second hiker did more work, because he walked the greater distance with his backpack. [3.7% picked]

(B) Neither. They did equal amounts of work on their backpacks. [91.8% picked]

(C) The first hiker, because he took less time to carry the backpack up the mountain. [0.4% picked]

(D) The first hiker, because he exerted the larger uphill force on his backpack. [4.1% picked]

Answer: (B) Neither. They did equal amounts of work on their backpacks. [91.8% picked]

Why: Video Discussion

Problem 4:

You are watching a baseball game and the pitcher has just thrown the ball toward the batter at home plate. Neglect any effects due to the air. Once the ball has left the pitcher's hand and is heading forward toward home plate, it experiences

(A) a forward horizontal force until it reaches the midpoint of its trip to home plate and then a backward horizontal force for the remainder of its trip. [0.0% picked]

(B) a forward horizontal force that remains constant all the way to home plate. [17.6% picked]

(C) a forward horizontal force that diminishes gradually as the ball approaches home plate. [8.2% picked]

(D) no horizontal force in the forward direction. [74.2% picked]

Answer: (D) no horizontal force in the forward direction. [74.2% picked]

Why: Video Discussion

Problem 5:

A heavy container of orange juice sits on the shelf of your refrigerator's door. That orange juice

(A) makes it harder to change the door's angular velocity. [93.4% picked]

(B) makes it easier to change the door's angular velocity. [0.4% picked]

(C) decreases the door's angular velocity. [4.1% picked]

(D) increases the door's angular velocity. [1.6% picked]

Answer: (A) makes it harder to change the door's angular velocity. [93.4% picked]

Why: Video Discussion

Problem 6:

A freestyle skier goes off a jump and does a back flip while separating her legs into a spread eagle. During the time that she is not touching the ground and neglecting any effects due to the air, the one aspect of her motion that is constant is her

(A) velocity. [0.8% picked]

(B) angular velocity. [14.3% picked]

(C) momentum. [7.8% picked]

(D) angular momentum. [76.6% picked]

Answer: (D) angular momentum. [76.6% picked]

Why: Video Discussion

Problem 7:

You are watching children play a game of tug-o-war with a plastic clothesline. The two teams are pulling at opposite ends of the cord and each team is trying to drag the other team into a mud puddle that lies between them. After a few minutes without progress, the team on the right suddenly pulls hard toward the right. The team on the left has anticipated this threat and is able to keep their end of the rope from moving. The right end of the rope stretches toward the right and the rope breaks. Breaking the rope required energy and that energy was provided by

(A) neither team. It was instead provided by chemical potential energy in the rope itself. [1.6% picked]

(B) both teams. [19.3% picked]

(C) the team on the left. [3.3% picked]

(D) the team on the right. [75.8% picked]

Answer: (D) the team on the right. [75.8% picked]

Why: Video Discussion

Problem 8:

You are riding a department store escalator from the first floor to the second floor. You are midway between floors and traveling uphill at constant velocity. The force that the escalator exerts on you points

(A) horizontally, in the forward direction. [1.6% picked]

(B) directly upward. [88.5% picked]

(C) uphill (toward the second floor exit of the escalator). [9.4% picked]

(D) downhill (toward the first floor entrance of the escalator). [0.4% picked]

Answer: (B) directly upward. [88.5% picked]

Why: Video Discussion

Problem 9:

You shoot a free throw at the basketball court and the ball travels in an arc toward the hoop. Neglecting any effects due to the air, the net force on the ball when it is midway between you and the hoop

(A) points up and away from you. [3.3% picked]

(B) is zero. [21.7% picked]

(C) points straight down. [62.7% picked]

(D) points down and away from you. [12.3% picked]

Answer: (C) points straight down. [62.7% picked]

Why: Video Discussion

Problem 10:

When you bounce a tennis ball off a concrete wall, the ball

(A) retains essentially all of its momentum but transfers a large amount of energy to the wall. [9.8% picked]

(B) retains essentially all of its energy but transfers a large amount of momentum to the wall. [81.1% picked]

(C) transfers a large amount of momentum and energy to the wall. [6.1% picked]

(D) retains essentially all of its energy and momentum. [2.9% picked]

Answer: (B) retains essentially all of its energy but transfers a large amount of momentum to the wall. [81.1% picked]

Why: Video Discussion

Problem 11:

You walk on a carpet and accumulate a large static charge. You touch a metal pot that's resting on an insulating plastic countertop and transfer some of your charge to the pot. When you remove your hand from the pot, the pot's charge is

(A) on its inner surface. [1.6% picked]

(B) on its outer surface. [91.0% picked]

(C) distributed throughout the metal. [7.0% picked]

(D) on both its outer and inner surfaces. [0.4% picked]

Answer: (B) on its outer surface. [91.0% picked]

Why: Video Discussion

Problem 12:

A xerographic copier uses a very thin wire with a large positive voltage to spray electric charges onto the surface of its photoconductor. That thin wire

(A) has a strong electric field near it and that strong field pushes charge from the wire onto air molecules. [66.4% picked]

(B) has a weak electric field near it and that weak field easily permits the transfer of charge from the wire to surface of the photoconductor. [18.0% picked]

(C) is able to move charge quickly enough to produce finely detailed light and dark spots on the copies. [11.5% picked]

(D) heats up quickly and boils off electric charge onto the surface of the photoconductor. [2.9% picked]

Answer: (A) has a strong electric field near it and that strong field pushes charge from the wire onto air molecules. [66.4% picked]

Why: Video Discussion

Problem 13:

A flashlight has two wires connecting its battery to its lightbulb. When you turn the flashlight off, the switch disconnects only one of those two wires. Disconnecting one wire stops the lightbulb from glowing because

(A) one wire carries only half as much current and that's not enough to light the lightbulb. [0.0% picked]

(B) two wires are needed to allow charge to move from the lightbulb to the battery. [0.0% picked]

(C) current can only flow continuously between the battery and lightbulb when one wire carries it to the lightbulb and another wire returns it to the battery. [98.4% picked]

(D) two wires are needed to allow charge to move from the battery to the lightbulb. [1.6% picked]

Answer: (C) current can only flow continuously between the battery and lightbulb when one wire carries it to the lightbulb and another wire returns it to the battery. [98.4% picked]

Why: Video Discussion

Problem 14:

A one-battery flashlight is turned on and is producing light. Current flows through its lightbulb from

(A) higher voltage to lower voltage. Current flows through its battery from lower voltage to higher voltage. [77.5% picked]

(B) lower voltage to higher voltage. Current flows through its battery from lower voltage to higher voltage. [2.0% picked]

(C) higher voltage to lower voltage. Current flows through its battery from higher voltage to lower voltage. [18.0% picked]

(D) lower voltage to higher voltage. Current flows through its battery from higher voltage to lower voltage. [2.5% picked]

Answer: (A) higher voltage to lower voltage. Current flows through its battery from lower voltage to higher voltage. [77.5% picked]

Why: Video Discussion

Problem 15:

A speedboat is pulling a water-skier with a rope and the skier is traveling forward in a straight line path at a constant speed. The net force experienced by the skier

(A) points in the forward direction. [20.9% picked]

(B) points in the backward direction. [2.0% picked]

(C) points in the upward direction. [1.2% picked]

(D) is zero. [75.0% picked]

Answer: (D) is zero. [75.0% picked]

Why: Video Discussion

Problem 16:

Two identical children run along a horizontal platform side by side and jump into a swimming pool at the same moment. They both jump equally hard, but one child jumps upward while the other child jumps forward. You watch them fall and see that

(A) the two children reach the water at the same moment and at the same distance from the pool's edge. [4.9% picked]

(B) the child who jumped upward reaches the water before the child who jumped forward. [0.0% picked]

(C) the child who jumped forward reaches the water before the child who jumped upward. [27.0% picked]

(D) the two children reach the water at the same moment and but the child who jumped forward travels farther from the pool's edge than does the other child. [67.6% picked]

Answer: (C) the child who jumped forward reaches the water before the child who jumped upward. [27.0% picked]

Why: Video Discussion

Problem 17:

When it is providing electric power to a lightbulb, a battery uses its chemical potential energy to

(A) create negative charge. [0.8% picked]

(B) pump positive charge from its positive terminal to its negative terminal. [12.3% picked]

(C) pump positive charge from its negative terminal to its positive terminal. [86.1% picked]

(D) create positive charge. [0.8% picked]

Answer: (C) pump positive charge from its negative terminal to its positive terminal. [86.1% picked]

Why: Video Discussion

Problem 18:

You are dragging an old carpet across the floor in a straight line at a steady speed. Which of the following statements about the forces acting on the carpet is correct?

(A) The amount of force that you're exerting on the carpet must be more than the amount of its weight. [2.0% picked]

(B) If you were to exert twice as much force on the carpet, it would slide across the floor twice as fast. [9.0% picked]

(C) The amount of force that you're exerting on the carpet must be equal to the amount of force that friction is exerting on it. [33.6% picked]

(D) The amount of force that you're exerting on the carpet must be more than the amount of force that friction is exerting on it. [54.9% picked]

Answer: (C) The amount of force that you're exerting on the carpet must be equal to the amount of force that friction is exerting on it. [33.6% picked]

Why: Video Discussion

Problem 19:

A plastic bag and a glass window are both electrically neutral. You hold the bag with insulating tongs and touch the bag to the window. The bag acquires a positive net charge. As you use the tongs to pull the bag away from the window, the voltage of bag

(A) increases and its net charge increases. [8.2% picked]

(B) increases, but its net charge remains constant. [77.5% picked]

(C) remains constant, but its net charge decreases. [10.2% picked]

(D) remains constant, but its net charge increases. [2.5% picked]

Answer: (B) increases, but its net charge remains constant. [77.5% picked]

Why: Video Discussion

Problem 20:

You have two bowling balls, one of which weighs twice as much as the other. The balls roll off a horizontal table at the same time and at the same velocity. In this situation, both balls hit the floor

(A) at approximately the same time, but the heavier ball hits considerably farther from the table than the lighter ball. [11.9% picked]

(B) at approximately the same distance from the table, but the heavier ball hits the floor well before the lighter ball [4.5% picked]

(C) at approximately the same time, but the lighter ball hits considerably farther from the table than the heavier ball. [39.3% picked]

(D) at approximately the same time and at the same distance from the table. [44.3% picked]

Answer: (D) at approximately the same time and at the same distance from the table. [44.3% picked]

Why: Video Discussion

Problem 21:

You are working out on an elliptical machine at the gym. This particular machine has handles that move away from you as you push them away from you and that move toward you as you pull them toward you. You are transferring energy to those handles

(A) whenever you are touching those handles. [3.3% picked]

(B) only as you push them away from you. [14.3% picked]

(C) only as you pull them toward you. [0.0% picked]

(D) as you push them away from you and as you pull them toward you. [82.4% picked]

Answer: (D) as you push them away from you and as you pull them toward you. [82.4% picked]

Why: Video Discussion

Problem 22:

A metal birdfeeder hangs from an insulating string and has zero net charge. You rub a toy balloon on your wool sweater, giving the balloon a negative net charge, and hold that balloon near the birdfeeder. The birdfeeder now

(A) has a positive net charge. [2.9% picked]

(B) is electrically polarized, with its positive end nearest the balloon. [88.9% picked]

(C) is electrically polarized, with its negative end nearest the balloon. [3.3% picked]

(D) has a negative net charge. [4.9% picked]

Answer: (B) is electrically polarized, with its positive end nearest the balloon. [88.9% picked]

Why: Video Discussion

Problem 23:

A rigid two-blade wind turbine that is experiencing zero net torque

(A) is motionless and horizontal. [9.0% picked]

(B) is motionless and may be horizontal or tilted. [23.0% picked]

(C) has a constant angular velocity. [66.4% picked]

(D) has an angular velocity that is gradually decreasing toward zero. [1.2% picked]

Answer: (C) has a constant angular velocity. [66.4% picked]

Why: Video Discussion

Problem 24:

You bicycling up a hill at constant velocity and the bicycle's pedals are turning at constant angular velocity. Compared to the torque you are exerting on those pedals with your feet, the torque that the bicycle's chain is exerting on those pedals is

(A) equal in amount but points in the opposite direction. [64.3% picked]

(B) smaller in amount. [3.7% picked]

(C) equal in amount and points in the same direction. [25.0% picked]

(D) greater in amount. [6.6% picked]

Answer: (A) equal in amount but points in the opposite direction. [64.3% picked]

Why: Video Discussion

Problem 25:

You are wearing roller skates. You board a bus and stand motionless in the aisle of the motionless bus. You are facing forward and not touching anything as the bus starts moving forward. You find yourself heading toward the back of the bus. What is causing you to head toward the back of the bus?

(A) The bus is exerting a frictional force on your skates. [5.3% picked]

(B) Your weight. [2.0% picked]

(C) The bus is exerting a support force on your skates. [1.2% picked]

(D) Inertia. [91.4% picked]

Answer: (D) Inertia. [91.4% picked]

Why: Video Discussion

Problem 26:

You are juggling grapefruits and you toss one straight up. Neglect any effects due to the air. After that grapefruit leaves your hand, it experiences

(A) a constant downward force, both as it rises and as it descends. [77.5% picked]

(B) a gradually decreasing upward force as it rises and a gradually increasing downward force as it descends. [18.0% picked]

(C) a constant upward force as it rises and a constant downward force as it descends. [1.6% picked]

(D) zero force as it rises and a constant downward force as it descends. [2.9% picked]

Answer: (A) a constant downward force, both as it rises and as it descends. [77.5% picked]

Why: Video Discussion

Problem 27:

Two children are sitting in a toy wagon. You are pulling that wagon forward on level ground and its speed is increasing. If you are exerting a forward force of 50 newtons on the wagon's handle, the wagon's handle is exerting a backward force of

(A) zero newtons on your hand. [0.8% picked]

(B) more than 50 newtons on your hand. [0.8% picked]

(C) somewhat less than 50 newtons on your hand. [20.9% picked]

(D) 50 newtons on your hand. [77.5% picked]

Answer: (D) 50 newtons on your hand. [77.5% picked]

Why: Video Discussion

Problem 28:

In a famous ice skating trick, a skater begins spinning with her arms out and then pulls her arms tightly against her body. She is then spinning extremely fast on the tip of one skate. Her angular velocity increases because her angular momentum

(A) is constant but her momentum decreases. [0.0% picked]

(B) decreases so she can spin faster. [2.9% picked]

(C) increases but her rotational mass remains constant. [8.6% picked]

(D) is constant but her rotational mass decreases. [88.5% picked]

Answer: (D) is constant but her rotational mass decreases. [88.5% picked]

Why: Video Discussion

Problem 29:

A quick trip down a plastic playground slide has caused a child's fine white-blond hair to begin standing straight up so that she looks like a dandelion puff. During the trip down the slide,

(A) contact between the slide and the girl transferred electric charge between the slide and girl so that one is positively charged and the other is negatively charged. [81.6% picked]

(B) friction between the slide and the girl gave them both negative net charges. [2.9% picked]

(C) friction between the slide and the girl gave them both positive net charges. [0.8% picked]

(D) contact between the slide and the girl polarized the girl so that she has negative charge on her hair and positive charge on her body. [13.9% picked]

Answer: (A) contact between the slide and the girl transferred electric charge between the slide and girl so that one is positively charged and the other is negatively charged. [81.6% picked]

Why: Video Discussion

Problem 30:

An acorn falls 20 meters from the high branch of an oak tree to the ground. This fall takes about 2 seconds. After it has fallen for only 1 second, the acorn is still falling and is located

(A) considerably more than 10 meters above the ground. [42.6% picked]

(B) considerably less than 10 meters above the ground. [7.4% picked]

(C) just a little less than 10 meters above the ground. [23.4% picked]

(D) 10 meters above the ground. [26.2% picked]

Answer: (A) considerably more than 10 meters above the ground. [42.6% picked]

Why: Video Discussion