PRINT AND BRING WITH YOU IN CLASS

Practice Midterm

Physics 14

Last Name_______________ First Name______________________

To get a full credit show the all calculations steps in the spaces provided. All work must be

shown in order to receive FULL credit.

1. Shown below is a speed-time graph for a cart moving in front of the motion

sensor. For convenience it has been divided into four sections (A,B,C,D).

During each of the four separate periods shown on the graph (A, B, C, D), was an

unbalanced force acting on the cart? YES or NO. If not, how can you tell from the

graph? If yes, did the unbalanced force act in the same direction as the cart’s motion,

or against it? Briefly explain how you can tell this from the graph.

A

B

C

D

2. A child playing with a toy car gives it a quick

shove on a smooth level floor. (The car does not have any type of motor inside it.) After his push, the car very gradually slows down and stops.

Four students are discussing why the car very gradually slows down and stops, after

the shove.

Kristen

Daryl

Samantha

Victor

The car slows down because

the force pushing it forward is

getting weaker and weaker.

It slows because, after the shove,

there is no more force to keep it

moving.

It slows down because the forces

acting on it are balanced, and balanced

forces make a moving object come to

rest.

The car slows down because there is

a force acting on it in the opposite

direction to its motion.

Which student do you agree with (if any)? Please explain your reasoning.

3. In the left column below there are three situations where a cart is acting on by more than one force. The direction and strength of each force is shown. In the second column state whether the forces acting on that cart are balanced or unbalanced. If balanced, leave the third column blank. If unbalanced, in the third column draw the net force on the cart (the single equivalent force) and make sure you include its direction and strength in N.

Object with forces acting on it Are forces

balanced or

unbalanced?

If unbalanced, draw the

net force

(a)

(b)

(c)

4. After starting the box moving the mother and child in the previous question want to make the box move across the floor at a certain constant speed. Which one of the following statements best describes what they should do to achieve this?

They should keep pushing with the same strength force they used to start the box

moving.

They should keep increasing the strength of their push until the box is moving at the

speed they want, then keep it at that strength.

When the box reaches the speed they want they should reduce the strength of their

push to exactly match the strength of the resisting force.

When the box reaches the speed they want they should stop pushing.

Please explain your reasoning

5. The famous chef, Antonio, is making pizza. He shapes the dough for the base into a

large round, flat shape, and then tosses it into the air. It rises about three feet before falling back down, where he catches it.

Which of the following diagrams best represents the forces acting on the pizza after it has reached its highest point and has begun falling back down. Circle your choice.

Explain your reasoning.

6. A boy has a ball in his hand. He then tosses the ball

straight upward. The ball rises to a certain height and then falls back down, and is caught by the boy again.

A.

B.

C.

D.

Below, sketch a speed-time graph for the entire history of the ball’s motion. Use the

following labels to show on the graph each separate part of the ball’s motion.

TOSSES RISES FALLS CAUGHT

a) Draw a force diagram for the ball for the part of the motion where it is being

tossed upwards. Make sure you label the force(s), pay attention to the length(s), and also include a motion arrow.

7. Consider two different carts that are designed to move along a surface with essentially no friction. Cart A is has more mass than cart B. A student performs two experiments with these carts.

In the first experiment she mounts identical

fans (with same number of batteries) on each of the two carts and puts the carts on separate tracks. She turns both fans on and lets the carts start moving at the same time. To the right is a force diagram (with motion arrow) for cart B one second after the carts begin moving:

Consider cart A (the more massive one). Suppose you wanted to draw a force diagram for cart A at the same time (one second after starting), including both a force arrow and a speed arrow:

a) Which of the following arrows could best represent the length of the force arrow

on cart A. Circle your choice and briefly justify why you made that choice.

b) Which of the following arrows could best represent the length of the speed arrow for cart A. Circle your choice and briefly justify why you made that choice.

MULTIPLE CHOICE. Choose the one alternative that best completes the

statement or answers the question. Circle the answer and mark this choice on the

scantron.

1) A sheet of paper can be withdrawn from under a container of milk without toppling

it if the paper is jerked quickly. This best demonstrates that

A) gravity tends to hold the milk carton secure.

B) there is an action-reaction pair of forces.

C) the milk carton has inertia.

D) the milk carton has no acceleration.

E) none of these

C

2) If no external forces are acting on a moving object, it will

A) move slower and slower until it finally stops.

B) continue moving at the same speed.

C) continue moving at the same velocity.

C

3) If a rocket initially at rest accelerates at a rate of 50 m/s2 for one minute, its speed

will be

A) 500 m/s. B) 50 m/s. C) 3600 m/s. D) 3000 m/s.

D

4) An apple falls from a tree and hits the ground 5 meters below. It hits the ground with

a speed of about

A) 20 m/s.

B) 15 m/s.

C) 10 m/s.

D) 5 m/s.

E) not enough information given to estimate

D

5) A ball tossed vertically upward rises, reaches its highest point, and then falls back to

its starting point. During this time the acceleration of the ball is always

A) in the direction of motion. B) directed downward.

C) directed upward. D) opposite its velocity.

B

6) Someone standing at the edge of a cliff throws one ball straight up and another ball

straight down at the same initial speed. Neglecting air resistance, the ball to hit the

ground below the cliff with the greater speed will be

A) the one thrown downward.

B) the one thrown upward.

C) neither -- they will both hit with the same speed.

C

7) If one object has twice as much mass as another object, it also has twice as much

A) velocity.

B) volume.

C) inertia.

D) acceleration due to gravity.

E) all of these

C

8) Strange as it may seem, it is just as hard to accelerate a car on a level surface on the

moon as it is here on the Earth. This is because

A) the weight of the car is independent of gravity.

B) the mass of the car is independent of gravity.

C) Nonsense! A car is much more easily accelerated on the moon than on the Earth.

B

9) A rock weighs 30 N on Earth. A second rock weighs 30 N on the moon. Which of the

two rocks has the greater mass?

A) the one on the moon B) the one on Earth

C) They have the same mass. D) not enough information to say

A

10) A 1-kg mass at the Earth's surface weighs

A) 10.8 N. B) 4.9 N. C) 9.8 N. D) 1 N. E) none of these

C

11) If the mass of an object does not change, a constant net force on the object

produces constant

A) velocity. B) acceleration. C) both of these D) neither of these

B

12) A 10-N block and a 1-N block lie on a horizontal frictionless table. To provide them

with equal horizontal acceleration, we would have to push with

A) 10 squared or 100 times as much force on the heavier block.

B) equal forces on each block.

C) 10 times as much force on the heavier block.

D) 1/10 as much force on the heavier block.

E) none of these

C

13) A heavy truck and a small car rolling down a hill at the same speed are forced to

stop in the same amount of time. Compared to the force that stops the car, the force

needed to stop the truck is

A) the same. B) greater. C) smaller.

B

14) A 10-kilogram block is pushed across a horizontal surface with a horizontal force of

20 N against a friction force of 10 N. The acceleration of the block in meters per second

per second is

A) 1. B) 2. C) 10. D) 5. E) none of these

A

15) A light woman and a heavy man jump from an airplane at the same time and open

their same-size parachutes at the same time. Which person will get to a state of zero

acceleration first?

A) the light woman B) the heavy man

C) Both should arrive at the same time. D) not enough information

A

16) A large and a small person wish to parachute at equal terminal velocities. The larger

person will have to

A) pull upward on the supporting strands to decrease the downward net force.

B) jump lightly.

C) jump first from the plane.

D) get a larger parachute.

D

17) A baseball player bats a ball with a force of 1000 N. The reaction force that the ball

exerts against the bat is

A) more than 1000 N. B) less than 1000 N.

C) 1000 N. D) impossible to determine.

C

18) A person is attracted toward the center of Earth by a 500-N gravitational force. The

Earth is attracted toward the person with a force of

A) 500 N. B) 250 N. C) zero. D) 1000 N.

A

19) A car traveling at 100 km/hr strikes an unfortunate bug and splatters it. The force

of impact is

A) greater on the car. B) the same for both. C) greater on the bug.

B

20) A 1-kg mass at the Earth's surface weighs

A) 10.8 N.

B) 4.9 N.

C) 9.8 N.

D) 1 N.

E) none of these

C

21) A 10-N block and a 1-N block lie on a horizontal frictionless table. To provide them

with equal horizontal acceleration, we would have to push with

A) 10 squared or 100 times as much force on the heavier block.

B) equal forces on each block.

C) 10 times as much force on the heavier block.

D) 1/10 as much force on the heavier block.

E) none of these

C

22) A skydiver of mass 100 kg experiences air resistance of 500 N, and an

acceleration of

A) about 0.3 g.

B) more than 0.5 g.

C) about 0.4 g.

D) about 0.2 g.

E) about 0.5 g.

E

23) A 10-kilogram block is pushed across a horizontal surface with a horizontal force of

20 N against a friction force of 10 N. The acceleration of the block in meters per second

per second is

A) 1.

B) 2.

C) 10.

D) 5.

E) none of these

A

24) A light woman and a heavy man jump from an airplane at the same time and open

their same-size parachutes at the same time. Which person will get to a state of zero

acceleration first?

A) the light woman B) the heavy man

C) Both should arrive at the same time. D) not enough information

A

25) A large and a small person wish to parachute at equal terminal velocities. The larger

person will have to

A) pull upward on the supporting strands to decrease the downward net force.

B) jump lightly.

C) jump first from the plane.

D) get a larger parachute.

D