Midterm Examination 1 Solutions

Problem 1:

You are walking a dog on a leash when a squirrel runs by. Suddenly, the two of you are accelerating forward. If the dog is exerting a 50 newton force forward on you, the force that you are exerting on the dog is

(A) more than a 50 newton force backward. [0.9% picked]

(B) less than a 50 newton force backward (but not zero). [17.0% picked]

(C) zero. [2.1% picked]

(D) a 50 newton force backward. [80.0% picked]

Answer: (D) a 50 newton force backward. [80.0% picked]

Why: Video Discussion

Problem 2:

A cat accidently tumbles off the deck in your backyard. As the cat falls, she flexes her body instinctively and manages to land on her feet. She is unharmed. During the time that the cat 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. [7.2% picked]

(B) angular momentum. [66.4% picked]

(C) angular velocity. [10.6% picked]

(D) momentum. [15.7% picked]

Answer: (B) angular momentum. [66.4% picked]

Why: Video Discussion

Problem 3:

You're late for a bowling tournament. The traffic light turns green and you stomp on the accelerator. Your bowling ball, which had been resting motionless on the floor beside you, suddenly rolls toward the back of your Porsche. What is causing the ball to move toward the back of car?

(A) Inertia. [91.1% picked]

(B) The car is exerting a frictional force on the ball. [2.6% picked]

(C) The ball's weight. [3.4% picked]

(D) The car is exerting a support force on the ball. [3.0% picked]

Answer: (A) Inertia. [91.1% picked]

Why: Video Discussion

Problem 4:

You are competing in an archery contest and have just released an arrow toward the target. Neglect any effects due to the air. Once the arrow has left the bow and is heading forward toward the target, it experiences

(A) a forward horizontal force that diminishes gradually as the arrow approaches the target. [6.4% picked]

(B) a forward horizontal force until it reaches the midpoint of its trip to the target and then a backward horizontal force for the remainder of its trip. [1.3% picked]

(C) a forward horizontal force that remains constant all the way to the target. [4.3% picked]

(D) no horizontal force in the forward direction. [88.1% picked]

Answer: (D) no horizontal force in the forward direction. [88.1% picked]

Why: Video Discussion

Problem 5:

You are playing baskeball. Occasionally the baskeball rolls all the way around the inside of the basket and then rolls out the top. The conserved quantity that it was unable to get rid of and that causes it to pop out of the basket is

(A) potential energy. [6.0% picked]

(B) momentum. [30.2% picked]

(C) energy. [41.7% picked]

(D) kinetic energy. [21.7% picked]

Answer: (C) energy. [41.7% picked]

Why: Video Discussion

Problem 6:

Your luxury apartment has a dining room table that is so enormous, it has a "lazy Susan" in the middle. This large circular platform rotates frictionlessly so that you can "pass" the marmalade jar to your guests by placing that jar on the platform and then rotating the platform. When you replace the empty jar with a full jar from the pantry, the full jar

(A) increases the platform's angular velocity. [6.0% picked]

(B) makes it harder to change the platform's angular velocity. [71.1% picked]

(C) decreases the platform's angular velocity. [21.7% picked]

(D) makes it easier to change the platform's angular velocity. [1.3% picked]

Answer: (B) makes it harder to change the platform's angular velocity. [71.1% picked]

Why: Video Discussion

Problem 7:

When a bicycle wheel is experiencing zero net torque, that wheel

(A) is motionless and its axle may be oriented in any direction. [11.1% picked]

(B) has an angular velocity that is gradually decreasing toward zero. [1.3% picked]

(C) has a constant angular velocity. [82.6% picked]

(D) is motionless and its axle is oriented vertically. [5.1% picked]

Answer: (C) has a constant angular velocity. [82.6% picked]

Why: Video Discussion

Problem 8:

As you sit in your chair, the amount of momentum you are transferring to the chair each second is equal to

(A) your weight times 1 second. [13.6% picked]

(B) zero. [61.7% picked]

(C) your weight divided by your mass. [3.8% picked]

(D) your mass times 1 second. [20.4% picked]

Answer: (A) your weight times 1 second. [13.6% picked]

Why: Video Discussion

Problem 9:

A lazy skateboarder is holding on to a bicyclist as the bicyclist pedals furiously. The pair is traveling up a smooth hill in a straight line path at a constant speed. The net force experienced by the skateboarder

(A) is zero. [86.0% picked]

(B) points in the forward direction. [6.8% picked]

(C) points in the upward direction. [3.0% picked]

(D) points in the backward direction. [3.4% picked]

Answer: (A) is zero. [86.0% picked]

Why: Video Discussion

Problem 10:

You are onstage to accept your second Oscar and you are so excited that you toss the little statue into the air. The audience gasps. After that statue leaves your hand, it experiences

(A) a constant downward force, both as it rises and as it descends. [86.4% picked]

(B) a gradually decreasing upward force as it rises and a gradually increasing downward force as it descends. [8.1% picked]

(C) a constant upward force as it rises and a constant downward force as it descends. [0.9% picked]

(D) zero force as it rises and a constant downward force as it descends. [4.7% picked]

Answer: (A) a constant downward force, both as it rises and as it descends. [86.4% picked]

Why: Video Discussion

Problem 11:

You make a sharp right turn in your new Ferrari and the bobble-head doll on your dashboard flies out the left side window. The doll's abrupt departure was caused by

(A) its inertia. [88.9% picked]

(B) its gravitational potential energy. [1.3% picked]

(C) a leftward force exerted on it by the dashboard. [2.6% picked]

(D) a leftward net force it experienced because of the car's velocity. [7.2% picked]

Answer: (A) its inertia. [88.9% picked]

Why: Video Discussion

Problem 12:

You and your friend carry identical water bottles from the first floor to the fifth floor. Your friend uses the stairs while you climb straight up the fire escape ladder. Which of you did the most work on your water bottle?

(A) Your friend did more work, because your friend walked the greater distance with the water bottle. [6.0% picked]

(B) You did more work, because you took less time to carry your water bottle from the first floor to the fifth floor. [1.7% picked]

(C) Neither. You did equal amounts of work on your water bottles. [85.5% picked]

(D) You did more work, because you exerted the larger upward force on your water bottle. [6.8% picked]

Answer: (C) Neither. You did equal amounts of work on your water bottles. [85.5% picked]

Why: Video Discussion

Problem 13:

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. [1.7% picked]

(B) uphill (toward the second floor exit of the escalator). [20.0% picked]

(C) downhill (toward the first floor entrance of the escalator). [4.7% picked]

(D) directly upward. [73.6% picked]

Answer: (D) directly upward. [73.6% picked]

Why: Video Discussion

Problem 14:

The only job you can find after graduation is with the music industry. No you're not the next Lady Gaga; you're simply looking for illegal downloaders. The good news is that you and your team get to use a battering ram to break down doors. You must design a 50-kilogram battering ram that exerts the largest possible force when it impacts the door and it must also transfer the largest possible momentum to the door. The part of the ram that hits door should be

(A) stiff and dead. [19.1% picked]

(B) stiff and lively. [71.1% picked]

(C) soft and lively. [8.5% picked]

(D) soft and dead. [1.3% picked]

Answer: (B) stiff and lively. [71.1% picked]

Why: Video Discussion

Problem 15:

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 force that friction is exerting on it. [11.1% picked]

(B) The amount of force that you're exerting on the carpet must be more than the amount of its weight. [0.9% picked]

(C) If you were to exert twice as much force on the carpet, it would slide across the floor twice as fast. [1.3% picked]

(D) 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. [86.4% picked]

Answer: (D) 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. [86.4% picked]

Why: Video Discussion

Problem 16:

You are holding a heavy bag of groceries in your hand as you bicycle at constant velocity along a horizontal road. While you hold up the bag, you are doing

(A) (positive) work on the bag and it is doing (positive) work on you. [4.3% picked]

(B) (positive) work on the bag and it is doing negative work on you. [36.6% picked]

(C) zero work on the bag and it is doing zero work on you. [55.7% picked]

(D) negative work on the bag and it is doing (positive) work on you. [3.0% picked]

Answer: (C) zero work on the bag and it is doing zero work on you. [55.7% picked]

Why: Video Discussion

Problem 17:

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. [0.4% picked]

(B) increases but her rotational mass remains constant. [8.9% picked]

(C) decreases so she can spin faster. [4.7% picked]

(D) is constant but her rotational mass decreases. [86.0% picked]

Answer: (D) is constant but her rotational mass decreases. [86.0% picked]

Why: Video Discussion

Problem 18:

You are playing dodge ball and there are two identical balls heading toward you at once. One is traveling at 10 km/h and the other at 100 km/h. The faster ball is carrying

(A) 121 times as much kinetic energy as the slower ball. [12.8% picked]

(B) 10 times as much kinetic energy as the slower ball. [34.5% picked]

(C) 100 times as much kinetic energy as the slower ball. [49.8% picked]

(D) 11 times as much kinetic energy as the slower ball. [2.1% picked]

Answer: (C) 100 times as much kinetic energy as the slower ball. [49.8% picked]

Why: Video Discussion

Problem 19:

You're filming a movie and you arrange for two unoccupied cars to drive horizontally off a tall cliff side-by-side at the same velocity. The Mercedes sedan weighs twice as much as the Mini Cooper. In this situation, the two cars hit the level ground below the cliff

(A) at approximately the same time and at the same distance from the cliff. [78.3% picked]

(B) at approximately the same time, but the Mini Cooper hits considerably farther from the cliff than the Mercedes sedan. [11.9% picked]

(C) at approximately the same distance from the cliff, but the Mercedes sedan hits much sooner than the Mini Cooper. [0.9% picked]

(D) at approximately the same time, but the Mercedes sedan hits considerably farther from the cliff than the Mini Cooper. [8.9% picked]

Answer: (A) at approximately the same time and at the same distance from the cliff. [78.3% picked]

Why: Video Discussion

Problem 20:

You are playing horseshoes and you have thrown your horseshoe toward the scoring pin. The horseshoe is traveling in an arc without touching anything and is now exactly midway between you and the pin. Neglecting any effects due to the air, the net force on the horseshoe at this moment

(A) is zero. [28.9% picked]

(B) points straight down. [59.1% picked]

(C) points up and away from you. [0.4% picked]

(D) points down and away from you. [11.5% picked]

Answer: (B) points straight down. [59.1% picked]

Why: Video Discussion

Problem 21:

A pole vaulter will bounce higher when he lands on a lively foam pad than when he lands on a concrete walkway. That's because

(A) the pole vaulter has more momentum when he hits the foam pad than when he hits the concrete walkway. [1.3% picked]

(B) the concrete walkway has more mass than the foam pad. [0.0% picked]

(C) the concrete walkway exerts less torque on the pole vaulter than the concrete walkway does. [0.4% picked]

(D) the foam pad deforms more as it slows the falling pole vaulter and it stores more of the collision energy. [98.3% picked]

Answer: (D) the foam pad deforms more as it slows the falling pole vaulter and it stores more of the collision energy. [98.3% picked]

Why: Video Discussion

Problem 22:

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. [5.1% picked]

(B) 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. [59.1% picked]

(C) the child who jumps upward reaches the water before the child who jumps forward. [1.7% picked]

(D) the child who jumps forward reaches the water before the child who jumps upward. [34.0% picked]

Answer: (D) the child who jumps forward reaches the water before the child who jumps upward. [34.0% picked]

Why: Video Discussion

Problem 23:

You have a midnight craving for ice cream and are walking quickly through your pitch-black apartment when you collide with the wall. You come to a complete stop. Fortunately, your roommate has mounted a thick woolen tapestry (wall-hanging) on the cement wall and that soft tapestry saves you from injury. When you came to a stop on the tapestry-covered wall, you transferred

(A) the same momentum to the tapestry-covered wall as you would have coming to a stop on the bare wall, but you did so with a larger force over a shorter period of time. [0.9% picked]

(B) more momentum to the tapestry-covered wall than you would have coming to a stop on the bare wall. [2.6% picked]

(C) less momentum to the tapestry-covered wall than you would have coming to a stop on the bare wall. [3.4% picked]

(D) the same momentum to the tapestry-covered wall as you would have coming to a stop on the bare wall, but you did so with a smaller force over a longer period of time. [93.2% picked]

Answer: (D) the same momentum to the tapestry-covered wall as you would have coming to a stop on the bare wall, but you did so with a smaller force over a longer period of time. [93.2% picked]

Why: Video Discussion

Problem 24:

To win a stuffed animal at the state fair, you simply need to drop a glass marble onto a stationary glass plate and have the marble come to rest on that plate. Unfortunately, when the marble hits the plate, it bounces upward because the marble

(A) retains essentially all of its energy but transfers a large amount of momentum to the plate. [70.6% picked]

(B) retains essentially all of its momentum but transfers a large amount of energy to the plate. [5.1% picked]

(C) transfers a large amount of momentum and energy to the plate. [4.7% picked]

(D) retains essentially all of its energy and momentum. [19.1% picked]

Answer: (A) retains essentially all of its energy but transfers a large amount of momentum to the plate. [70.6% picked]

Why: Video Discussion

Problem 25:

To see what it's like to bungee jump, you attach a huge rubber band to the roof of your porch and hold on to the other end of the band as you jump off the porch. Not surprisingly, the band stretches to its limit and then snaps. Breaking that rubber band required energy and that energy was provided by

(A) neither you nor the porch roof. It was instead provided by chemical potential energy in the rubber band itself. [4.7% picked]

(B) you, but not the porch roof. [80.0% picked]

(C) both you and the porch roof. [14.5% picked]

(D) the porch roof, but not you. [0.4% picked]

Answer: (B) you, but not the porch roof. [80.0% picked]

Why: Video Discussion

Problem 26:

Your laptop falls off the shelf onto your bed and bounces up and down before settling motionless at equilibrium on the mattress. Fortunately, it's undamaged and you can still spend all your time on Facebook. When during the laptop's descent does it first stop accelerating downward?

(A) Just before it touches the mattress for the first time. [2.1% picked]

(B) When it reaches its lowest point of the first bounce and is deep in the mattress. [30.6% picked]

(C) When it touches the mattress for the first time. [13.6% picked]

(D) When it is at equilibrium on the mattress for the first time. [53.6% picked]

Answer: (D) When it is at equilibrium on the mattress for the first time. [53.6% picked]

Why: Video Discussion

Problem 27:

You jump while standing on a bathroom scale and the scale briefly reads more than your actual weight. During that moment, the scale is exerting an upward force on you that is

(A) equal to your weight and you are accelerating upward. [1.7% picked]

(B) greater than your weight and you are accelerating upward. [90.2% picked]

(C) greater than your weight and your velocity is constant. [6.0% picked]

(D) equal to your weight and your velocity is constant. [2.1% picked]

Answer: (B) greater than your weight and you are accelerating upward. [90.2% picked]

Why: Video Discussion

Problem 28:

You drop a baseball from the top of a tall building and it hits the ground 4 seconds later. When the baseball has fallen for only 2 seconds, how far is it above the ground? [Note: neglect any effects due to the air.]

(A) It is about 3/4 the height of the building. [35.7% picked]

(B) It is a little less than 1/2 the height of the building. [23.4% picked]

(C) It is a little more than 1/2 the height of the building. [18.7% picked]

(D) It is about 1/2 the height of the building. [22.1% picked]

Answer: (A) It is about 3/4 the height of the building. [35.7% picked]

Why: Video Discussion

Problem 29:

A wind turbine is turning at constant angular velocity and generating electric power. Compared to the torque that the wind is exerting on that turbine to the torque the generator is exerting on that turbine. [Note: neglect friction or any other nuisance effects.]

(A) The torque the generator exerts is smaller in amount than the torque the wind exerts. [6.8% picked]

(B) The torques are equal in amount and point in the same direction. [11.1% picked]

(C) The torque the generator exerts is larger in amount than the torque the wind exerts. [4.7% picked]

(D) The torques are equal in amount but point in the opposite directions. [77.0% picked]

Answer: (D) The torques are equal in amount but point in the opposite directions. [77.0% picked]

Why: Video Discussion

Problem 30:

You are kneading a large portion of bread dough with your hands. You push the top of the dough away from you as it squishes away from you and you pull the top of the dough toward you as it squishes toward you. You are transferring energy to the bread dough

(A) only as you push it away from you. [15.7% picked]

(B) whenever you are touching the bread dough. [7.7% picked]

(C) only as you pull it toward you. [0.9% picked]

(D) as you push it away from you and as you pull it toward you. [75.7% picked]

Answer: (D) as you push it away from you and as you pull it toward you. [75.7% picked]

Why: Video Discussion