Phys 151 Midterm Conceptual Problems

1. Consider a ball thrown straight up in the air. At what position is its kinetic energy at a maximum? a. as soon as it leaves the hand b. halfway up and rising c. at the zenith d. halfway up and falling 2. Where is its gravitational potential energy at a maximum? a. as soon as it leaves the hand b. halfway up and rising c. at the zenith d. halfway up and falling

1. A 2. C

1. Strictly speaking, as more and more skyscrapers are built on the surface of the Earth, does the day tend to become longer or shorter? a. The day tends to become shorter. b. The length of the day is unchanged. c. The day tends to become longer. 2. And strictly speaking, does the falling of autumn leaves tend to lengthen or shorten the 24-hour day? a. Falling leaves shorten the 24-hour day. b. Falling leaves would not affect the length of the day. c. Falling leaves lengthen the 24-hour day.

1. C 2. A

1. If a Mack truck and Honda Civic have a head-on collision, upon which vehicle is the impact force greater? a. The force on the Mack truck is greater. b. The force on the Honda Civic is greater. c. The force on both vehicles is the same. 2. Which vehicle experiences the greater acceleration? a. The acceleration of the Mack truck is greater. b. The acceleration of the Honda Civic is greater. c. The acceleration of both vehicles is the same.

1. C 2. B

1. If a Mack truck and a Ford Escort have a head-on collision, which vehicle will experience the greater force of impact? a. the Mack truck b. the Ford Escort c. both experience the same force 2. Which vehicle will experience the greater impulse? a. the Mack truck b. the Ford Escort c. both experience the same impulse 3. Which vehicle will experience the greater change in momentum? a. the Mack truck b. the Ford Escort c. both experience the same change in momentum 4. Which vehicle will experience the greater acceleration? a. the Mack truck b. the Ford Escort

1. C 2. C 3. C 4. B

1. Does the speed of a falling object depend on its mass? Yes No 2. Does the speed of a satellite in orbit depend on its mass? Yes No

1. No 2. No

1. If an automobile had a 100% efficient engine, transferring all of the fuel's energy to work, would the engine be warm to your touch? Yes No 2. Would its exhaust heat the surrounding air? Yes No 3. Would it make any noise? Yes No 4. Would it vibrate? Yes No 5. Would any of its fuel go unused? Yes No

1. No 2. No 3. No 4. No 5. No

1. Does the string that supports a pendulum bob do work on the bob as it swings to and fro? Yes No 2. Does the force of gravity do any work on the bob? Yes No

1. No 2. Yes

1. Two lumps of clay with equal and opposite momenta have a head-on collison and come to rest. Is momentum conserved? Yes No 2. Is kinetic energy conserved? No Yes

1. Yes 2. No

1. If you were in a car that drove off the edge of a cliff, would you be momentarily weightless? Yes No 2. Would gravity still be acting on you? Yes No

1. Yes 2. Yes

An automobile speedometer is configured to read speed proportional to the rotational speed of its wheels. If larger wheels, such as those of snow tires, are used, will the speedometer reading be high or low - or no different? a. The speedometer will read too low. b. The speedometer will read the same. c. The speedometer will read too high.

A

Consider the identical balls released from rest on Tracks A and B as shown. When they reach the right ends of the tracks, which will have the greater speed? a. The ball on track A will have the greater speed. b. The ball on track B will have the greater speed. c. Both will have the same speed. d. There is not enough information to decide.

A

Does the KE of a car change more when it goes from 10 to 20 km/h or when it goes from 20 to 30 km/h? a. The KE changes more from 20 to 30 km/h. b. The KE changes more from 10 to 20 km/h. c. The KE change is the same for both cases.

A

Ken and Joanne are astronauts floating some distance apart in space. They are joined by a safety cord whose ends are tied around their waists. If Ken starts pulling on the cord, will he pull Joanne toward him, or will he pull himself toward Joanne, or will both astronauts move? a. Both will move. b. Ken will pull himself toward Joane. c. Ken will pull Joanne toward him.

A

Suppose that the three balls shown in the figure below start simultaneously from the tops of the hills. Which one reaches the bottom first? A.) the middle (concave) hill B.) the right (convex) hill C.) the left (straight) hill

A

The Earth and the moon are attracted to each other by gravitational force. Does the more massive Earth attract the less massive moon with a force that is greater, smaller, or the same as the force with which the moon attracts the Earth? (With an elastic band stretched between your thumb and forefinger, which is pulled more strongly by the band, your thumb or your forefinger?) a. The Earth and moon pull equally on each other. b. The moon pulls on the Earth with a greater force. c. The Earth pulls on the moon with a greater force. d. The answer depends on the phase of the moon

A

The centers of gravity of the three trucks parked on a hill are shown by the X's. Which truck(s) will tip over? a. the leftmost truck b. the middle truck c. the rightmost truck d. none of the trucks

A

Two 100 N weights are attached to a spring scale as shown. Does the scale read 0, 100, or 200 N, or give some other reading? (Hint: Would it read any differently if one of the ropes were tied to the wall instead of to the hanging 100 N weight?) a. 100 N b. 200 N c. 0 N d. some other reading

A

Would a head-on collision between two cars be more damaging to the occupants if the cars stuck together or if the cars rebounded upon impact? a. More damage results if the cars rebound. b. More damage results if the cars stick together.

A

In the absence of air resistance, if a ball is thrown vertically upward with a certain initial speed, on returning to its original level it will have the same speed. When air resistance is a factor, will the ball be moving faster, the same, or slower than its throwing speed when it gets back to the same level? A.) slower B.) faster C.) same speeed Why?

A, The ball gain's speed until the air resistance is equals to its weight. Then, acceleration will stop and the ball will fall at a constant speed.

If a ball is thrown vertically into the air in the presence of air resistance, would you expect the time during which it rises to be longer or shorter than the time during which it falls? (Again use the "principle of exaggeration.") A.) The ball rises in less time than it falls. B.) The ball falls in less time than it rises. C.) The ball rises and falls in the same time. Explain.

A, The ball takes less time to rise with the presence of air resistance as long as the motion of the ball is strictly vertical.

(a) Can an object be moving when its acceleration is zero? If so, give an example. (b) Can an object be accelerating when its speed is zero? If so, give an example

A.) Yes, An example is a car moving at a constant speed. When there is no acceleration an object at rest will stay at rest, and an object in motion will stay in motion. B.)Yes, A ball at its peak after being thrown up in the air, its speed is 0 and its acceleration is gravity downwards.

A space probe may be carried by a rocket into outer space. What keeps the probe going after the rocket no longer pushes it?

An object in motion will stay in motion unless acted upon by an outside force.

Somewhere between the Earth and the moon, gravity from these two bodies on a space pod would cancel. Is this location nearer the Earth or the moon? a. nearer the earth b. nearer the moon c. exactly halfway

B

You sit at the middle of a large turntable at an amusement park as it is set spinning and then allowed to spin freely. When you crawl toward the edge of the turntable, does the rate of the rotation increase, decrease, or remain unchanged? a. The rate of rotation increases. b. The rate of roration decreases. c. The rate of rotation remains unchanged.

B

Harry and Sue cycle at the same speed. The tires on Harry's bike are larger diameter than those on Sue's bike. Which wheels, if either have the greater rotational speed? a. Both have the same rotational speed. b. Harry's tires have the greater rotational speed. c. Sue's tires have the greater rotational speed.

C

In the absence of air resistance, a ball thrown vertically upward with a certain initial KE will return to its original level with the same KE. When air resistance is a factor affecting the ball, will it return to its original level with the same, less, or more KE? a. more KE b. the same KE c. less KE

C

On which of these hills does the ball roll down with increasing speed and decreasing acceleration along the path? (Use this example if you wish to explain to someone the difference between speed and acceleration.) A.) the right (convex) hill B.) the left (straight) hill C.) the middle (concave) hill

C

Someone standing at the edge of a cliff (as in the figure) throws a ball nearly straight up at a certain speed and another ball nearly straight down with the same initial speed. If air resistance is negligible, which ball will have the greater speed when it strikes the ground below? A.) The ball thrown upward will strike at a greater speed. B.) The ball thrown downward will strike at a greater speed. C.) Both will strike the ground below at the same speed.

C

Suppose two carts, one twice as massive as the other, fly apart when the compressed spring that joins them is released. How fast does the heavier cart roll compared with the lighter cart? a. one quarter as fast b. four times as fast c. half as fast d. twice as fast e. the same speed

C

Which will have the greater acceleration rolling down an incline - a bowling ball or a volleyball? a. The volleyball wins. b. It will be a tie. c. The bowling ball wins.

C

Is the force of gravity stronger on a piece of iron than a piece of wood if both have the same mass? Yes No

No

Does a stick of dynamite contain force? Y/N Explain.

No, Force is an interaction between two objects.

If you drop an object, its acceleration toward the ground is 10 m/s2. If you throw it down instead, would its acceleration after throwing be greater than 10 m/s2? Y/N Why or Why not?

No, It would be in free fall.

Push a cart and it moves. When you stop pushing, it comes to a rest. Does this violate Newton's law of inertia? Y/N

No.

Can the velocity of an object reverse direction while maintaining a constant acceleration? Y/N Defend your Answer.

Yes, A net force will change velocity, and velocity is made up of both direction and speed. So a curved trajectory requires some force because direction changes.

On a long alley a bowling ball slows down as it rolls. Is any horizontal force acting on the ball? Y/N How do you know?

Yes, its the force of friction.

The strong man will push the two initially stationary freight cars of equal mass apart before he himself drops straight to the ground. a. Is it possible for him to give either of the cars a greater speed than the other? Y/N

a. No

Which of the following are scalar quantities, which are vector quantities, and which are neither? (a) velocity (b) age (c) color (d) speed (e) acceleration (f) shape (g) temperature

a. Vector b. Scalar c. Neither d. Scalar e. Vector f. Neither g. Scalar

Consider the two forces acting on the person who stands still, namely, the downward pull of gravity and the upward support of the floor. a. Are these forces equal and opposite? Y/N b. Do they form an action-reaction pair? Y/N

a. Yes b. No

You are driving north on a highway. Then, without changing speed, you round a curve and drive east. (a) Does your velocity change? (b) Do you accelerate? Y/N

a. Yes b. Yes

Why are thick floor mats used by gymnasts?

thicker mats cause momentum to change over a greater time which reduces force