Midterm Examination 1

Physics 1060 - Spring 2017 - Midterm Exam 1 - Posted Version

Problem 1:

You are graduating! As your degree is conferred, you grab hold of your mortarboard (hat) and throw it straight up into the air! At the moment your hat reaches peak height,

(A) the hat's acceleration is downward and its velocity is zero.

(B) the hat's acceleration is zero and its velocity is downward.

(D) the hat's acceleration is zero and its velocity is zero.

Problem 2:

To open a jar of honey, your right hand twists the jar's lid in one direction while your left hand twists the jar itself in the other direction. Unfortunately, the lid is stuck and remains motionless. The net torque on the lid is

(A) zero.

(B) equal to the torque your left hand is exerting on the jar.

(D) equal to the torque your right hand is exerting on the lid.

Problem 3:

You are at a roof party on a 40-story office building, when you accidently knock a rare plant off a ledge. The plant begins to fall and will hit the sidewalk, 122 m (400 ft) below, in 5.0 seconds if you don't catch it. Fortunately, you are exceptionally fast. You race down the stairs to a lower floor and catch the plant through an open window, only 2.5 seconds after it began falling. On which floor did you catch the plant?

(A) The 30^th floor, 92 m (300 ft) above the sidewalk.

(B) The 20^th floor, 61 m (200 ft) above the sidewalk.

(D) The 21^st floor, 64 m (210 ft) above the sidewalk.

Problem 4:

A squirrel completes an amazing leap between two trees. While the squirrel was not touching anything and neglecting any effects due to the air, one aspect of the squirrel's motion that must remain constant was its

(A) angular momentum.

(B) velocity.

(D) angular velocity.

Problem 5:

Your bicycle is stopped at an intersection. The light turns green and, as you begin to pedal, the bicycle accelerates forward along the level roadway. What is causing the bicycle to accelerate forward?

(A) The pedals are exerting a forward torque on the bicycle frame.

(B) Your feet are exerting forward forces on the bicycle pedals.

(D) Your pedaling is generating momentum and the force of that momentum pushes you forward.

Problem 6:

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 girl jumps mostly upward while the boy jumps mostly forward. After they leave the dock,

(A) the two children reach the water at the same moment, but the boy travels farther from the dock than does the girl.

(B) boy reaches the water before the girl.

(D) girl reaches the water before the girl.

Problem 7:

What is true about the electric field around a positively charged metal ball?

(A) That electric field points toward the ball and it becomes weaker as the distance from the ball increases.

(B) That electric field points away from the ball and it becomes stronger as the distance from the ball increases.

(D) That electric field points away from the ball and it becomes weaker as the distance from the ball increases.

Problem 8:

You hold a positively charged stick near a glass ball and then near a metal ball. What force does the charged stick experience in these two cases?

(A) The charged stick is attracted to both the glass ball and the metal ball.

(B) The charged stick is attracted to the glass ball but it is repelled by the metal ball.

(D) The charged stick is attracted to the glass ball but not to the metal ball.

Problem 9:

You are collecting wood for your campfire and are dragging a log toward the campfire at constant velocity. The net force on the log

(A) points upward and toward the campfire (at an angle between the two individual directions).

(B) points horizontally toward the campfire.

(D) points downward and toward the campfire (at an angle between the two individual directions).

Problem 10:

Suppose a piece of plastic has a positive charge of 1 coulomb. If you cut the piece in half, each half will have a positive charge of about 1/2 coulomb. If you keep subdividing the pieces, they'll keep getting smaller and with less charge. What is the smallest amount of positive charge one of those pieces can possibly have?

(A) The amount of positive charge on an atom.

(B) There is no limit to how small the positive charge can get.

(D) The amount of positive charge on the nucleus of an atom.

Problem 11:

Highway work trucks often have large crushable yellow "impact attenuator" boxes mounted on their rear bumpers. Suppose your forward-moving car collides with the rear end of a motionless truck and that the massive truck doesn't move at all during the impact. Compared to hitting the truck's immovable bumper, how does hitting the crushable box "attenuate" the impact? [Assume your car comes to a complete stop in either case. Neglect effects due to friction and the air.]

(A) Your car transfers all of its forward momentum to the attenuator box, but with a smaller force over a longer time. Your car transfers most of its energy to the truck in either case.

(B) Your car transfers all of its forward momentum to the attenuator box, but with a smaller force over a longer time. Your car transfers much of its energy to the attenuator box, whereas it cannot transfer energy to the truck bumper.

(C) Your car transfers less forward momentum to the attenuator box than it would to the truck bumper and more force remains in the car.

(D) Your car transfers more forward momentum to the attenuator box than it would to the truck bumper and less force remains in the car.

Problem 12:

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) No. It can only be equal in amount to the ball's weight.

(B) Yes. It can be greater than the ball's weight. It cannot be less than the ball's weight.

(D) Yes. It can be less than the ball's weight. It cannot be greater than the ball's weight.

Problem 13:

You can open a swinging door (see figure) by pushing it in the middle (Point A, located 1 foot from the hinges) or at the edge farthest from the hinges (Point B, located 2 feet from the hinges). If you exert a 10-newton force on the door, perpendicular to its surface, how will your choice of Point A or Point B affect the door's motion?

(A) Pushing on Point B will cause twice the angular acceleration as compared to pushing on Point A.

(B) Pushing on Point B will cause half the angular acceleration as pushing on Point A.

(D) Pushing on Point B will cause half the angular velocity as pushing on Point A.

Problem 14:

You and a wrapped gift are both electrically neutral. You remove the plastic wrapper from the gift and find that the wrapper is now clinging to your hand. Why?

(A) The wrapper and gift acquired equal but opposite charges when you separated them. The charged wrapper has polarized your hand and is attracted to that polarization.

(B) The wrapper and gift acquired equal but opposite charges when you separated them. The wrapper has given half of its charge to your hand, so the wrapper and your hand now attract one another.

(C) Both the wrapper and your hand are electrically neutral, so they don't repel. The opposite of repulsion is attraction, so the wrapper and your hand must attract one another.

(D) As you moved the wrapper farther from the gift, the wrapper's charge increased and some of that charge began to jump onto your hand. Your charged hand now attracts the charged wrapper.

Problem 15:

A child on tricycle loses control and begins to roll down a hill. You come to the rescue, pushing the child uphill to slow the child to a stop. While the child was rolling toward you and slowing down, how did the force you exerted on the child compare to the force the child exerted on you?

(A) The force you exerted on the child was greater than the force the child exerted on you.

(B) You exerted a force on the child, but the child did not exert a force on you.

(D) The force you exerted on the child was less than the force the child exerted on you.

Problem 16:

There are two metal spheres on your desk, one on the left and one on the right (see figure). Someone has attached a battery to those spheres, so the sphere on the left has a voltage of +5 volts and the sphere on the right has a voltage of –5 volts. Midway between the two spheres, the electric field points

(A) upward.

(B) downward.

(D) toward the left.

Problem 17:

A racquetball court has rigid, immovable walls. You hit the rubber ball forward, toward the front wall of the court, and the ball bounces back at you. Before hitting the wall, the ball carried both energy and forward momentum. During its bounce, the ball transferred to the wall

(A) all of its energy and all its forward momentum.

(B) no energy and more forward momentum than it had before the bounce.

(D) all of its energy and no momentum.

Problem 18:

Taken together, your Styrofoam coffee cup and its plastic lid are electrically neutral. When you remove the lid from the cup, the lid has a positive charge and the cup has a negative charge. As you pull the lid farther away from the cup, what happens to the lid? [neglect any effects due to your hands or the air]

(A) The lid's charge increases.

(B) The lid's voltage increases.

(D) The lid's charge decreases.

Problem 19:

You are pulling a toy wagon up a ramp that rises vertically 1 meter for every 8 meters you travel uphill along its surface (see figure). If you let go of the wagon, how will it move? [neglect friction and effects due to the air]

(A) It will move downhill at a constant velocity.

(B) It will accelerate downhill at 1/4^th the acceleration due to gravity.

(D) It will accelerate downhill at 1/2^th the acceleration due to gravity.

Problem 20:

You are watching two puppies fight over a rubber toy. The puppy on the right pulls its end of the toy toward the right while the puppy on the left pulls its end of the toy toward the left. Suddenly, the puppy on the right pulls its end of the toy violently toward the right while the puppy on the left keeps its end of the toy from moving. The toy breaks into two pieces. Breaking the toy required energy and that energy was provided by

(A) the puppy on the right.

(B) neither puppy. It was instead provided by chemical potential energy in the toy itself.

(D) the puppy on the left.

Problem 21:

A 10-car passenger train is moving uphill on a smooth ramp at a constant velocity. The net force on the last car of that train is

(A) non-zero and points at an angle between directly uphill (along the ramp) and directly upward (vertical).

(B) zero.

(D) non-zero and points directly upward (vertical).

Problem 22:

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) decreases so she can spin faster.

(B) is constant but her momentum decreases.

(D) increases but her rotational mass remains constant.

Problem 23:

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

(A) no horizontal force in the forward direction.

(B) a forward horizontal force that remains constant all the way to home plate.

(D) 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.

Problem 24:

Two cars collide gently in a parking lot, damaging their bumpers. How do the two cars' total (combined) momentum and kinetic energy compare before and after the collision? [neglect friction and air effects, and assume the parking lot is otherwise empty and level.]

(A) The cars have the same total momentum before and after, but they have less total kinetic energy after the collision.

(B) The cars have less total momentum after the collision, but they have the same total kinetic energy before and after.

(D) The cars have less total momentum after the collision and they have less total kinetic energy after the collision.

Problem 25:

You are sitting in the lobby of a hotel, watching 4 people who are wearing backpacks. Which person is doing work on their backpack?

(A) The person who is riding down an escalator at constant velocity toward the lobby.

(B) The person who is riding upward at constant velocity in a glass elevator.

(C) The person at the reception desk, who has removed her backpack and is lowering that backpack toward the floor at constant velocity.

(D) The person who is walking at constant velocity across the lobby floor.

Problem 26:

A sharp metal pin has a voltage of +1000 volts and it points toward a wide metal surface with a voltage of –1000 volts (see figure). What is the voltage midway between the surface and the pin?

(A) A positive voltage greater than +1000 volts.

(B) A positive voltage less than +1000 volts.

(D) 0 volts.

Problem 27:

A positively 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?

(A) The car's charge cannot be determined without measuring it.

(B) The car is electrically neutral.

(D) The car is negatively charged.

Problem 28:

A helicopter is carrying you from the base of a mountain to a resort on the mountaintop. The helicopter is traveling along a straight-line path at a steady speed. The force that the helicopter exerts on you points

(A) upward (vertically).

(B) toward the mountaintop resort.

(D) at an angle that points slightly above the mountaintop resort.

Problem 29:

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.

(B) The angular velocity of your arm must be greater than the angular velocity of your friend's arm.

(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.

Problem 30:

A particular 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 strong electric field near it and that strong field pushes positive charge from the wire onto air molecules.

(B) 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.

(D) heats up quickly and boils off electric charge onto the surface of the photoconductor.