Physics 105 - How Things Work - Fall, 2003

Problem 1:

When a sport utility vehicle (SUV) makes a sudden left turn on the highway, it is in danger of flipping over. One valid explanation for this effect is:

(A) the SUV's angular mass increases as it turns and its angular momentum decreases. A transfer of angular momentum from its wheels to its frame then causes it to begin rotating so that it flips over.

(B) the centrifugal force on the SUV as it goes around the turn pushes outward on the top of the SUV. The wheels are held in place by friction, so only the top of the SUV accelerates outward and it flips over.

(C) the force of the SUV's momentum pushes it forward while the road pushes it to the left and these two forces twist the SUV so that it undergoes angular acceleration and flips over.

(D) the leftward frictional force that causes the SUV to accelerate leftward during the turn also exerts a torque on the SUV about its center of mass and can cause the SUV to undergo angular acceleration and flip over.

Problem 2:

You and your friend slap your right hands together in "high fives"--your hands make a loud noise, but neither hand is able to push the other hand forward during the slap. Overall the two of you exchange

(A) both energy and momentum.

(B) neither energy nor momentum.

(C) momentum but no energy.

(D) energy but no momentum.

Problem 3:

Jumping from your balcony into the swimming pool will hurt less than an identical jump onto the pool's concrete deck because the impulse (momentum transfer) you will experience when hitting the water will be

(A) the same as when hitting the deck, but will involve a smaller force for a longer time.

(B) smaller than when hitting the deck and will involve a smaller force for a longer time.

(C) smaller than when hitting the deck and will involve a smaller force for the same time.

(D) larger than when hitting the deck, but will involve a smaller force for a smaller time.

Problem 4:

If you hit the sealed top of a glass bottle full of root beer, Pepsi, or Coke with a rubber mallet, the glass will accelerate downward while the beverage remains in place. The beverage will soon find itself in the neck of the bottle, compressing the gas there. The resulting pressure imbalance will accelerate the beverage toward the bottom of the bottle. When the beverage reaches the bottom of the bottle, it will

(A) knock the bottom out of the bottle.

(B) have already slowed to a stop and nothing dramatic will happen.

(C) emit a piercing whistling sound because of its angular momentum.

(D) blow the cap off the bottle.

Problem 5:

You are standing still in an elevator, with a briefcase hanging from your motionless hand. As the elevator rises toward the top of the building, you are doing

(A) zero work on the briefcase and the elevator is doing zero work on you.

(B) (positive) work on the briefcase and the elevator is zero work on you.

(C) zero work on the briefcase and the elevator is doing (positive) work on you.

(D) (positive) work on the briefcase and the elevator is doing (positive) work on you.

Problem 6:

You roll a marble down the side of a round bowl--a bowl with a spherical bottom. The marble rolls right through the bottom of the bowl and up the far side. At this moment, the marble is exactly at the bottom of the bowl. It is rolling away from you -- it has just rolled down your side of the bowl and is about to begin rolling up the far side of the bowl [added words]. It is accelerating

(A) downward.

(B) forward.

(C) upward

(D) backward.

Problem 7:

You are running in a race and are trying to catch up to the lead runner. According to the spectators, the lead runner is traveling at 10 mph (miles-per-hour) and you are traveling in same direction at 11 mph. From your perspective or "frame-of-reference", the lead runner is moving

(A) toward you at 1 mph.

(B) away from you at 1 mph.

(C) toward you at 21 mph.

(D) away from you at 21 mph.

Problem 8:

You are standing at the top of a tall cliff above a calm lake. You have two stones in your hand, one twice as heavy as the other, and you throw them together horizontally at the same speed. Both stones soon hit the water. Neglecting any air resistance, the heavier stone reaches the water

(A) in half the time and half as far from the cliff as the lighter stone.

(B) in half the time but at the same place as the lighter stone.

(C) at the same time but half as far from the cliff as the lighter stone.

(D) at the same time and at the same place as the lighter stone.

Problem 9:

A fast-moving softball is heading directly toward the pitcher after being hit by the batter. As it travels forward, the softball is experiencing

(A) a forward force that is equal to its momentum.

(B) a forward force that is equal to the square root of its momentum.

(C) a forward force that is equal to 1 divided by its momentum.

(D) zero forward force.

Problem 10:

You are heading straight forward on a bicycle when you and the bicycle accidentally begin leaning toward the left. The bicycle responds automatically and prevents you from tipping over by

(A) developing a restoring force toward the right that pushes you back toward your upright stable equilibrium.

(B) using its gravitational potential energy to push you back toward your upright stable equilibrium.

(C) using its elastic potential energy to push you back toward your upright stable equilibrium.

(D) steering toward the left and driving its wheels under your overall center of gravity.

Problem 11:

You're playing volleyball with friends and the ball is passing you on its way toward the other team. It isn't going fast enough, so you reach out and push the ball toward the other team. The force you exert on the moving volleyball is 1 pound. The force that volleyball exerts on you in return is

(A) more than 1 pound.

(B) 1 pound.

(C) less than 1 pound, but more than zero.

(D) zero.

Problem 12:

You are holding your friend's new television motionless in your hands while she fumbles in her purse for the keys to her apartment. Beads of sweat are dripping down your face. While you stand there like this, you are

(A) doing negative work on the television and it is doing (positive) work on you.

(B) doing (positive) work on the television.

(C) doing negative work on the television and it is doing negative work on you.

(D) doing zero work on the television.

Problem 13:

You are riding your bicycle on a smooth horizontal road when you drive over a bump. You are thrown briefly into the air. While your bicycle is not touching the road, you are

(A) not accelerating as you rise, but are accelerating downward as you descend back to the pavement.

(B) accelerating upward as you rise and downward as you descend back to the pavement.

(C) accelerating downward.

(D) not accelerating.

Problem 14:

When water from a hose flows steadily and frictionlessly through a nozzle, its total energy

(A) remains unchanged, but its pressure drops and its speed increases.

(B) remains unchanged, but both its pressure and speed increase.

(C) decreases, but its pressure and speed both increase.

(D) increases as its speed increases.

Problem 15:

Your tiny Italian sports car collides with a city bus. Your car's velocity changes abruptly and you drive into a haystack. The bus barely accelerates at all. Fortunately, no one is hurt. The momentum your car received during the collision was

(A) zero, because no distance was traveled by your car during the collision itself.

(B) greater than the momentum the bus lost during the collision.

(C) equal to the momentum the bus lost during the collision.

(D) less than the momentum the bus lost during the collision, but more than zero.

Problem 16:

You have a stiff, 1-liter bottle full of helium. You add some more helium to that bottle, but its temperature and volume remain unchanged. As a result of this addition, the bottle's pressure

(A) increases, its weight increases, but the buoyant force on it remains the same.

(B) and weight remain the same, but the buoyant force on it increases.

(C) remains the same, but its weight increases and the buoyant force on it increases.

(D) increases, its weight decreases and the buoyant force on it increases.

Problem 17:

A baby's sipping cup has a round bottom with a weight inside it. The cup always returns to upright, even after you tip it over. As you tip the cup, its center of gravity

(A) rises and its kinetic energy increases.

(B) descends and its total potential energy decreases.

(C) descends and its kinetic energy increases.

(D) rises and its total potential energy increases.

Problem 18:

You are riding a roller coaster and are upside-down at the very top of its loop-the-loop. You are traveling fast and you feel pressed into your seat. At this moment, you are accelerating

(A) backward.

(B) forward.

(C) downward.

(D) upward.

Problem 19:

You are designing a 2-foot high access ramp for a new library. One group wants a shorter ramp to save space. Another group wants to minimize the uphill force needed to push a wheelchair steadily up the ramp. If you double the ramp's length, the required uphill force will

(A) be reduced by half, but the product of that force times the ramp's length will remain unchanged.

(B) remain the same, but the product of that force times the ramp's travel time will be reduced by half.

(C) remain the same, but the product of that force times the ramp's length will be reduced by half.

(D) be reduced by half, but the product of that force times the ramp's travel time will remain unchanged.

Problem 20:

A heavy vase rests motionless on the floor. The vase is experiencing its weight downward and an equally strong force upward from the floor. We know that these two forces on the vase are equal in amount but oppositely directed because

(A) for every action, there is an equal but oppositely directed reaction.

(B) the vase has zero velocity.

(C) Newton's third law requires that forces always appear in equal but oppositely directed pairs.

(D) the vase is not accelerating so the two forces must sum to zero.

Problem 21:

The air inside your friend's hot air balloon is always heated to the same temperature, regardless of the weather. On a hot day, her balloon can carry

(A) more weight than it can on a cold day.

(B) the same weight that it can on a cold day.

(C) less weight than it can on a cold day.

(D) a complete line of fashion accessories.

Problem 22:

When you drop a bouncy ball onto the sandy beach, the normally "lively" ball barely bounces at all. The non-lively sand dominates this bouncing process because it receives most of the collision energy and then wastes that energy as thermal energy. The sand receives most of the collision energy because

(A) while the ball and sand push equally hard on one another, the ball dents more during the collision.

(B) the ball pushes harder on the sand than the sand pushes on the ball.

(C) while the ball and sand push equally hard on one another, the sand dents more during the collision.

(D) the sand pushes harder on the ball than the ball pushes on the sand.

Problem 23:

You are swinging a bucket full of water around you in a big horizontal circle at a constant speed [added words].. You are at the center of its circular path. The net force on the bucket points directly

(A) along the bucket's velocity (along its direction of travel).

(B) downward.

(C) away from you.

(D) toward you.

Problem 24:

You drop a bouncy ball on a granite floor and the ball bounces back almost to its original height. During the bounce, the ball and the floor exchanged

(A) considerable energy but almost zero momentum.

(B) considerable energy and momentum.

(C) considerable momentum but almost zero energy.

(D) almost zero momentum and almost zero energy.

Problem 25:

In certain situations, the flow of a liquid breaks up into turbulent swirls and eddies. This transition to turbulence depends in part on the liquid's density (its mass-per-volume) and its viscosity (the measure of its "thickness" or "syrupiness.") The liquid is most likely to become turbulent when it is moving

(A) slowly, has a low density, and a low viscosity.

(B) slowly, has a high density, and a high viscosity.

(C) fast, has a low density, and a high viscosity.

(D) fast, has a high density, and a low viscosity.

PART II: SHORT ANSWER QUESTIONS

Please give a brief answer in the space provided. Part II is worth 33% of the grade on the midterm examination.

Problem 1:

Some pranksters have "decorated" the trees in front of your neighbor's house with toilet paper. It's much easier to throw the paper into the trees than to remove it, so you are being a good friend and helping him remove it. You are using a garden hose and a nozzle to spray water at the paper hanging in the trees. Unfortunately, the paper is high up and the spray of water is having trouble reaching it.

(A) You find that the spray goes highest when you adjust the nozzle so that the amount of water it releases is relatively small. Why does letting much more water flow through the hose reduce the maximum height of the spray?

(B) The water jet rises 60 feet above the nozzle, which isn't quite high enough. You climb a 10-foot stepladder, but now the jet rises only 50 feet above the nozzle and the water peaks at the same altitude as before. Why?

(C) You borrow an electric water pump from another neighbor and increase the pressure of water in the hose. The water jet now rises much higher and you succeed in clearing the paper from the trees. Why did this water pump have to be plugged into the electric socket, instead of using the water passing through the pump to power itself?

(D) When the rising jet of water hits the paper, it pushes the paper away from it. In free flight, the water is at atmospheric pressure. What is the water's pressure where it hits the paper?

Problem 2:

A tall flagpole sits motionless and perfectly upright on a calm summer day. Suddenly, a flying Frisbee hits the flagpole hard near its top and it begins swaying back and forth rhythmically--toward you and away from you. Let's neglect air resistance or any forms of friction, so the flagpole will sway like this forever.

(A) When during its swaying is the flagpole accelerating toward you the fastest?

(B) When during its swaying is the flagpole moving toward you the fastest? (i.e. has its maximum velocity toward you.)

(C) When during its swaying does the flagpole have its lowest amount of total potential energy?

(D) When during its swaying does the flagpole have its largest amount of momentum toward you?

Problem 3:

You are trying to develop a computer-guided baseball glove. This glove should catch the ball on its own after you throw the glove into the air. Unfortunately, the conserved quantities of physics are preventing the glove from working well. [Assume the air exerts no forces or torques on the glove and that the glove remains a single, intact object.]

(A) You find that the computerized glove cannot rise any higher than a similarly thrown ordinary glove. Which conserved physical quantity prevents the glove from going higher and why can't the glove get more of it while in the air?

(B) You find that the computerized glove follows the same arcing path through space as a similarly thrown ordinary glove. Which conserved physical quantity is determining the glove's path through space and, neglecting the effects of gravity, why can't the glove get more of it while in the air?

(C) You find that if the computerized glove leaves the player's hand without any angular velocity (i.e. not spinning in any way), that it behaves just like a similarly thrown ordinary glove: neither one can start itself spinning. Which conserved physical quantity is determining the glove's spin and why can't the glove get more of it while in the air?

(D) Finally a small victory: if the computerized glove is thrown so that it is spinning, it can alter its angular velocity even though nothing is touch it. What does it do to change its angular velocity?