PHYS 1060 Spring 2015 - Midterm 1

Two identical metal sheets are glued to opposite sides of insulating glass plate and they are lying flat on an insulating table. The voltage of the top sheet is 0 volts and the voltage of the bottom sheet is 9 volts. The electric field between the sheets at their center points in which direction?

In a tower construction crane, a huge metal beam sits atop a vertical metal tower. The beam extends outward from the tower in two directions and it pivots about the top of the tower. A lifting cable hangs from one end of the beam and heavy weights hang from the other end of the beam. Since the lifting cable end of the beam is the only end that seems to do anything, what useful purpose does the weight-end of the beam serve?

(A) The beam pivots about its geometrical center, so it needs both ends in order for that geometrical center to be located above the tower. [4.3% picked]

(B) The weight-end of the beam places the beam's center of gravity at that end and thus makes the beam more stable. [3.0% picked]

(C) The weight-end of the beam ensures that the beam is approximately balanced about its pivot and experiences approximately zero torque due to gravity. [80.3% picked]

(D) The weight-end of the beam makes the beam more responsive to torques so that the crane operator can make it undergo more rapid angular accelerations about its pivot. [12.4% picked]

Answer: (C) The weight-end of the beam ensures that the beam is approximately balanced about its pivot and experiences approximately zero torque due to gravity. [80.3% picked]

You are camping in the woods on a dark night and you accidentally walk into tree. You come to a complete stop. Fortunately, the tree's hard, smooth bark was covered with soft moss. Why was being stopped by the moss-covered tree less painful than being stopped by a hard, smooth-barked tree?

(A) You would have transferred the same momentum to either tree, but you transferred that momentum more quickly to the moss-covered tree than you would have to the hard, smooth-barked tree. [1.7% picked]

(B) You would have transferred more momentum to the hard, smooth-barked tree than you did to the moss-covered tree. [0.4% picked]

(C) You would have transferred the same momentum to either tree, but you transferred that momentum more slowly to the moss-covered tree than you would have to the hard, smooth-barked tree. [97.4% picked]

(D) You would have transferred less momentum to the hard, smooth-barked tree than you did to the moss-covered tree. [0.4% picked]

Answer: (C) You would have transferred the same momentum to either tree, but you transferred that momentum more slowly to the moss-covered tree than you would have to the hard, smooth-barked tree. [97.4% picked]

Pedaling your bicycle provides power to its rear wheel and propels your bicycle forward. What force(s) is principally responsible for the bicycle's forward acceleration as you pedal your bicycle forward from rest on a level (horizontal) road?

(B) The pavement exerts forward frictional forces on the bottoms of the front and rear wheels. [33.3% picked]

Answer: (A) The pavement exerts a forward frictional force on the bottom of the rear wheel. [54.7% picked]

You're at the lake and watch two children jump off a dock. They jump at the same time and at the same speed, but the boy jumps mostly upward while the girl jumps mostly forward. After they leave the dock,

(B) the two children reach the water at the same moment, but the girl travels farther from the dock than does the boy. [9.0% picked]

(D) the two children reach the water at the same moment and at the same distance from the dock. [0.4% picked]

Which force is your weight? [The force that is your weight and not a force that is equal to your weight.]

(A) The force you exert on a trampoline as you land on that trampoline after jumping high above the trampoline's surface. [5.1% picked]

(B) The force that causes you to accelerate downward when you are high above the surface of a trampoline. [38.9% picked]

Answer: (B) The force that causes you to accelerate downward when you are high above the surface of a trampoline. [38.9% picked]

You've learned to juggle 4 balls at once here on Earth. During a visit to the moon, where the acceleration due to gravity is about 1/6th its Earth value, you decide to try juggling those same 4 balls. You find that, on the moon, each ball has

(A) less weight and falls more slowly than on Earth. It undergoes the same acceleration as on Earth when exposed to the same force as on Earth. [51.1% picked]

(B) the same weight and falls at the same rate as on Earth. It accelerates more slowly than on Earth when exposed to the same force as on Earth. [1.7% picked]

(C) less weight and falls more slowly than on Earth. It accelerates more rapidly than on Earth when exposed to the same force as on Earth. [22.7% picked]

(D) the same weight, but falls more slowly than on Earth. It accelerates more slowly than on Earth when exposed to the same force as on Earth. [24.5% picked]

Answer: (A) less weight and falls more slowly than on Earth. It undergoes the same acceleration as on Earth when exposed to the same force as on Earth. [51.1% picked]

You are riding on a large carousel at an amusement park and are enjoying the moving scenery as the carousel spins about its center of rotation. The ride comes to an end and the carousel gradually slows to a stop. Why does it take so long for the carousel to stop rotating?

(A) The spinning carousel has a large rotational mass and changing a large rotational mass requires a long time. [43.2% picked]

(B) The spinning carousel carries a large amount of angular momentum and the angular impulse needed to remove that angular momentum with a reasonable torque requires a long time. [50.0% picked]

(C) The spinning carousel has a large angular impulse and changing a large angular impulse requires a long time. [0.0% picked]

(D) The spinning carousel has a large angular velocity and changing a large angular velocity requires a long time. [6.8% picked]

Answer: (B) The spinning carousel carries a large amount of angular momentum and the angular impulse needed to remove that angular momentum with a reasonable torque requires a long time. [50.0% picked]

You are arm-wrestling another friend and find that you are almost perfectly matched. Your pair of arms is vertical and motionless, even though you are both trying hard to win. To begin winning, you want that pair of arms to rotate counterclockwise from your perspective. What must you do to make that happen?

(A) The torque you exert on your friend's arm must be greater in amount than the torque your friend exerts on your arm. [26.1% picked]

(B) The angular velocity of your arm must be greater than the angular velocity of your friend's arm. [2.1% picked]

(C) The angular acceleration of your arm must be greater than the angular acceleration of your friend's arm. [8.1% picked]

(D) The counterclockwise torque you exert on the pair of arms must be greater in amount than the clockwise torque your friend is exerting on that pair. [63.7% picked]

Answer: (D) The counterclockwise torque you exert on the pair of arms must be greater in amount than the clockwise torque your friend is exerting on that pair. [63.7% picked]

A toy top is a disk-shaped object with a sharp point and a thin stem projecting from its bottom and top, respectively. When you twist the stem hard, the top begins to spin rapidly. When you then set the top's point on the ground and let go of it, it continues to spin about a vertical axis for a very long time. What keeps the top spinning?

(B) The ground exerts an upward support force on the top that keeps the top spinning. [2.6% picked]

While searching for your keys, you place your cup of coffee on the roof of your parked car. Unfortunately, you forget about the coffee and climb into the car without it. As you start driving the car forward, you hear the coffee hit the ground behind the car. Why didn't the coffee stay on the roof of the car?

(B) The car's roof pushed the coffee backward, in the direction opposite the car's velocity. [0.9% picked]

(C) The coffee's inertia kept it essentially motionless as the car accelerated forward and left the coffee behind. [95.7% picked]

(D) The car's roof pushed the coffee backward, in the direction opposite the car's acceleration. [3.0% picked]

Answer: (C) The coffee's inertia kept it essentially motionless as the car accelerated forward and left the coffee behind. [95.7% picked]

When an archer sends an arrow toward a target, the archer must aim the arrow above the target's bullseye (its center) in order for the arrow to hit that bullseye. If the archer uses a stronger bow and therefore a faster-moving arrow, how will that change how the archer aims the arrow in order to hit the same target's bullseye? [Neglect any effects due to air]

(A) The archer must still aim above the target's bullseye, but farther above the bullseye than with the slower-moving arrow. [3.0% picked]

(B) The archer must still aim above the target's bullseye, but less far above the bullseye than with the slower-moving arrow. [82.5% picked]

Answer: (B) The archer must still aim above the target's bullseye, but less far above the bullseye than with the slower-moving arrow. [82.5% picked]

Which of the following is experiencing zero net force?

(A) A child who is riding a carousel (a merry-go-round) and is traveling around in a circle at a steady pace. [6.8% picked]

(C) A passenger in an elevator that is slowing down after its trip from the ground floor to the 10th floor. [1.3% picked]

(D) A water-skier who is being pulled forward by a speedboat and is moving in a straight-line path at a steady speed. [91.9% picked]

Answer: (D) A water-skier who is being pulled forward by a speedboat and is moving in a straight-line path at a steady speed. [91.9% picked]

A downhill skier is descending a snow-covered mountain. The skier steps off of a level region of the mountain and onto a steep slope. The skier begins to accelerate rapidly downhill on the slope. What force is causing the skier to accelerate downhill?

(A) The downhill ramp force that is the sum of the skier's weight and the support force exerted on the skier by the snow-covered slope. [52.1% picked]

Answer: (A) The downhill ramp force that is the sum of the skier's weight and the support force exerted on the skier by the snow-covered slope. [52.1% picked]

As a ball bounces on the floor, the floor exerts an upward support force on the ball. Can the amount of that upward support force on the ball be different from the ball's weight?

(A) Yes. It can be greater than the ball's weight and it can be less than the ball's weight. [22.2% picked]

(B) Yes. It can be less than the ball's weight. It cannot be greater than the ball's weight. [2.6% picked]

(D) Yes. It can be greater than the ball's weight. It cannot be less than the ball's weight. [42.7% picked]

Answer: (A) Yes. It can be greater than the ball's weight and it can be less than the ball's weight. [22.2% picked]

You are walking at constant velocity on a sidewalk that slopes gently uphill. What force(s) is the sidewalk exerting on you?

(B) A support force directed perpendicular to the sidewalk's surface, but no frictional force. [17.9% picked]

(C) A frictional force directed uphill, parallel to the sidewalk's surface, and a support force directed perpendicular to the sidewalk's surface. [57.7% picked]

Answer: (C) A frictional force directed uphill, parallel to the sidewalk's surface, and a support force directed perpendicular to the sidewalk's surface. [57.7% picked]

You are in an ordinary room (both its floor and ceiling are horizontal). You throw a ball directly upward and it bounces off the ceiling. While the ball is touching the ceiling, in which direction is the ceiling's support force on the ball?

(B) The ceiling's support force on the ball is directed upward while the ball is moving upward and is directed downward while the ball is moving downward. [1.7% picked]

(D) The ceiling's support force on the ball is directed downward while the ball is moving upward and is directed upward while the ball is moving downward. [5.6% picked]

Walking on ice can be treacherous. In general, you are less likely to slip and fall if you lower your foot vertically into place on the ice as you take each step than you are if you slide your foot horizontally into place on the ice as you take each step. Why is the vertical landing method of walking on ice usually safer than the horizontal sliding method?

(A) The static frictional forces you can obtain from the ice using the vertical landing method are larger, and more effective at preventing sideways slips, than the sliding friction forces you are likely to obtain from the ice using the horizontal sliding method. [77.4% picked]

(B) The vertical landing method increases your mass and makes it harder for you to accelerate sideways and slip. [3.0% picked]

(C) The vertical landing method increases your weight and makes it harder for you to accelerate sideways and slip. [3.0% picked]

(D) The vertical landing method increases the support forces the ice exerts on you and larger support forces can prevent you from slipping sideways and falling. [16.7% picked]

Answer: (A) The static frictional forces you can obtain from the ice using the vertical landing method are larger, and more effective at preventing sideways slips, than the sliding friction forces you are likely to obtain from the ice using the horizontal sliding method. [77.4% picked]

A paper canister of raisins has a plastic lid. Before you open the canister, the entire system (canister and lid) is electrically neutral. You remove the lid and find that it has a negative charge. Assuming that you did not exchange any charge with the system, what charge does the canister have? [The raisins are included in the canister.]

A metal ball has a negative charge. The voltage of the metal ball is

You walk on a carpet and accumulate a large static charge. If you reach out to a metal file cabinet with your finger, you'll receive a strong shock. Instead, you reach out to the file cabinet with a sharp metal needle in your hand, pointing that needle toward the file cabinet. As the needle moves toward the file cabinet, you receive

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

(A) has a weak electric field near it and that weak field easily permits the transfer of charge from the wire to the surface of the photoconductor. [1.3% picked]

(B) is able to move charge quickly enough to produce finely detailed light and dark spots on the copies. [3.0% picked]

(D) has a strong electric field near it and that strong field pushes charge from the wire onto air molecules. [93.6% picked]

Answer: (D) has a strong electric field near it and that strong field pushes charge from the wire onto air molecules. [93.6% picked]

A diver stands upright at the edge of the 10 meter platform at the Olympics. She jumps off the platform, folds into a ball shape, completes 3.5 somersaults, unfolds, and plunges head-first into the water. While she is not touching anything, which of the following physical quantities is constant? [Neglect any effects due to the air.]

A tall luxury hotel has a rotating restaurant at its top. The disk-shaped floor of the restaurant rotates slowly about the center of the restaurant and completes one full rotation every 30 minutes. When the restaurant opens each day, the manager turns on the motors that make the restaurant spin, but it takes several minutes for the restaurant to begin spinning at its full angular velocity. Why doesn't the restaurant reach full speed immediately?

(B) The restaurant has a large rotational mass that resists rapid angular accelerations. [91.0% picked]

(D) The restaurant has a large rotational mass that resists large angular velocities. [6.4% picked]

Answer: (B) The restaurant has a large rotational mass that resists rapid angular accelerations. [91.0% picked]

You are talking on your cellphone and you accidentally ride your bicycle off the road. You realize that you are going to collide with either a tree or a garbage can, so you must choose which object to hit. The tree will not move at all if you hit the tree, but the garbage can will move if you hit the garbage can. How will your choice of object affect the energy you transfer to that object when you hit it? [Fortunately, you are going slowly, so you won't be injured regardless of your choice.]

(A) You will transfer energy regardless of your choice, but you will transfer more energy if you hit the tree than if you hit the garbage can. [21.8% picked]

(B) You will transfer energy if you hit the garbage can, but you will not transfer energy if you hit the tree. [32.5% picked]

(C) You will transfer energy regardless of your choice, but you will transfer more energy if you hit the garbage can than if you hit the tree. [9.8% picked]

(D) Regardless of which object you hit, the amount of energy you transfer to the object will be the same. [35.9% picked]

Answer: (B) You will transfer energy if you hit the garbage can, but you will not transfer energy if you hit the tree. [32.5% picked]

To win a big prize at the fair or festival, all you have to do is toss a basketball into a bucket a few feet in front of you and have it remain in the bucket. The rigid bucket cannot move and it opens toward you, so the basketball will roll out of it unless the basketball settles in it just right. You try many times to get the basketball to stay in the bucket, but it keeps bouncing out. Why is it so difficult for the basketball to come to rest in the bucket?

(A) The basketball can transfer its momentum to the bucket, but it cannot transfer its energy to the bucket. [76.5% picked]

(C) The basketball can transfer its energy to the bucket, but it cannot transfer its momentum to the bucket. [17.9% picked]

Answer: (A) The basketball can transfer its momentum to the bucket, but it cannot transfer its energy to the bucket. [76.5% picked]

When you drive a car on a level (horizontal) road that is slippery with ice, you usually have no problems except when you try to speed up, slow down, or turn. Why does the icy road make those three actions hazardous? [neglect any effects due to air]

(A) Those three actions require the icy roads to exert support forces on the car's wheels. [0.9% picked]

(B) Those three actions require the icy roads to exert frictional forces on the car's wheels. [89.7% picked]

Answer: (B) Those three actions require the icy roads to exert frictional forces on the car's wheels. [89.7% picked]

A meteor is streaking toward city hall and will hit the building in a few second. As it moves through the sky, what physical quantities is the meteor carrying with it? [Ignore any effects due to air or Earth's gravity]

A negatively charged storm cloud is passing overhead as you step into your car in the middle of an open field. For the brief moment while you are touch both the ground and the car, electric charge can move between the ground and car. When you are completely inside the car and the car's tires insulate it from the ground, what is the car's electric charge?

You are dragging a heavy chair across the floor and that chair is moving toward the east at constant velocity. The net force on the chair

(A) points downward and eastward (at an angle between the two individual directions). [0.9% picked]

Physics 1060 - Spring 2015 - Midterm Exam 1 - Posted Version with Solutions