Download Force Practice

Honors Physics
Forces Review and Practice
Name: ___________________________
Multiple Choice
Identify the choice that best completes the statement or answers the question.
1. The law of inertia states that an object
a. will continue moving at the same velocity unless an outside force acts on it.
b. will continue moving in a straight line unless an outside force acts on it.
c. that is not moving will never move unless a force acts on it.
d. at rest will remain at rest unless acted on by an outside force.
e. will do all of the above.
2. The law of inertia applies to
a. objects at rest.
b. moving objects.
c. both moving and nonmoving objects.
3. An object following a straight-line path at constant speed
a. has no forces acting on it.
b. has a net force acting on it in the direction of motion.
c. has zero acceleration.
d. must be moving in a vacuum.
e. none of the above
4. One object has twice as much mass as another object. The first object also has twice as much
a. velocity.
b. gravitational acceleration.
c. inertia.
d. all of the above
5. You and a friend are jumping on a trampoline. Why does Earth, which is rapidly orbiting around the sun, not move under
your feet when you jump?
a. There are different rules in space and on the surface of the earth
b. Newton’s first law holds that your body moves along with Earth because it is not compelled to change its motion by
an unbalanced force.
c. Newton’s second law holds that the acceleration produced by the force of gravity is offset by the force of friction on
your feet.
d. Newton’s third law holds that there is an equal and opposite force exerted by the trampoline on your feet, which
allows you to move with Earth through space.
6. After a cannonball is fired into frictionless space, the amount of force needed to keep it going equals
a. zero, since no force is necessary to keep it moving.
b. twice the force with which it was fired.
c. one half the force with which it was fired.
d. the same amount of force with which it was fired.
e. one quarter the force with which it was fired.
7. If the force of gravity suddenly stopped acting on the planets, they would
a. spiral slowly towards the sun.
b. continue to orbit the sun.
c. move in straight lines tangent to their orbits.
d. spiral slowly away from the sun.
e. fly straight away from the sun.
8. A sheet of paper can be withdrawn from under a container of milk without toppling it if the paper is jerked quickly. The
reason this can be done is that
a. gravity pulls very hard on the milk carton.
b. the milk carton has very little weight.
c. the milk carton has inertia.
d. none of the above
9. A 3 N force accelerates a 3 kg mass at the rate of 1 m/s2. The acceleration of a 6 kg mass acted upon by a 6 N force is
a. twice as much.
b. half as much.
c. the same.
d. none of the above
10. A box is dragged without acceleration in a straight-line path across a level surface by a force of 13 N. What is the
frictional force between the box and the surface?
a. 13 N
b. Less than 13 N
c. More than 13 N
d. Need more information to say.
11. A 20-N falling object encounters 4 N of air resistance. The magnitude of the net force on the object is
a. 0 N.
b. 4 N.
c. 16 N.
d. 20 N.
e. none of the above
12. You pull horizontally on a 50-kg crate with a force of 450 N and the friction force on the crate is 250 N. The acceleration
of the crate is
a. 2 m/s2.
b. 4 m/s2.
c. 9 m/s2.
d. 14 m/s2.
13. How does acceleration of an object change in relation to its mass? It is
a. directly proportional.
b. Acceleration doesn't depend on mass at all.
c. inversely proportional.
14. A 10-kg brick and a 1-kg book are dropped in a vacuum. The force of gravity on the 10-kg brick is
a. 10 times as much as the force on the 1-kg book.
b. zero.
c. the same as the force on the 1-kg book.
15. If you pull horizontally on a desk with a force of 150 N and the desk doesn't move, the friction force must be 150 N. Now
if you pull with 250 N so the desk slides at constant velocity, the friction force is
a. more than 150 N but less than 250 N.
b. 250 N.
c. more than 250.
16. If the force acting on a cart doubles, what happens to the cart's acceleration?
a. It quarters.
b. It halves.
c. It stays the same.
d. It doubles.
e. It quadruples.
17. Suppose a cart is being moved by a force. If suddenly a load is dumped into the cart so that the cart's mass doubles, what
happens to the cart's acceleration?
a. It quarters.
b. It halves.
c. It stays the same.
d. It doubles.
e. It quadruples.
18. A 6-N falling object encounters 6 N of air resistance. The magnitude of the net force on the object is
a. 0 N.
b. 6 N.
c. 12 N.
d. none of the above
19. Forces always occur
a. as single quantities.
b. by themselves.
c. in pairs.
d. in triplets.
20. A player catches a ball. Consider the action force to be the impact of the ball against the player's glove. What is the
reaction to this force?
a. The muscular effort in the player's arms
b. The force the glove exerts on the ball
c. Friction of the ground against the player's shoes
d. The player's grip on the glove
e. none of the above
21. As a ball falls, the action force is the pull of Earth's mass on the ball. What is the reaction to this force?
a. The pull of the ball's mass on Earth
b. The acceleration of the ball
c. Nonexistent in this case
d. Air resistance acting against the ball
e. none of the above
22. An unfortunate bug splatters against the windshield of a moving car. Compared to the force of the car on the bug, the
force of the bug on the car is
a. larger.
b. the same.
c. smaller.
d. Need more information to say
23. If a horse pulls on a wagon at rest, the wagon pulls back equally on the horse. Can the wagon be set into motion?
a. Yes, because there is a net force acting on the wagon.
b. Yes, because there is a time delay between action and reaction.
c. No, because the forces cancel each other.
d. Yes, because the horse's pull on the wagon is larger than the wagon's pull on the horse.
24. A large truck and a small car traveling at the same speed have a head-on collision. The vehicle to undergo the greater
change in velocity will be
a. the small car.
b. the large truck.
c. neither—both are the same
25. A person is attracted towards the center of Earth by a 440-N gravitational force. The force with which Earth is attracted
toward the person is
a. 440 N.
b. very very small.
c. very very large.
26. An unfortunate bug splatters against the windshield of a moving car. Compared to the deceleration of the car, the
deceleration of the bug is
a. larger.
b. the same.
c. smaller.
27. A rocket is able to accelerate in the vacuum of space when it fires its engines. The force that propels the rocket is the
force
a. of the rocket on the exhaust gases.
b. of the exhaust gases on the rocket.
c. neither A nor B
Short Answer/Discussion Questions
1.
Jacob gives his skateboard a push and it rolls across the classroom floor. Emily says that after it leaves Jacob’s hand,
his force remains with it, keeping it going. Sophia disagrees and says that Jacob’s push gives the skateboard speed,
not force, and that when his hand is no longer in contact with it the force is no more. Who do you agree with and
why?
2.
Terry says that if an object has no acceleration, then no forces are exerted on it. Sherry doesn’t agree but can’t
provide an explanation. They both look to you. What do you say?
3.
In a vacuum, a coin and a feather fall side by side. Would it be correct to say that in a vacuum equal force of gravity
acts on both the coin and the feather?
4.
Consider the two forces acting on a person who stands still, namely, the downward pull of gravity and the upward
support of the floor. Are these forces equal and opposite? Do they comprise an action-reaction pair? Why or why
not?
5.
A small car bumps into a van at rest in a parking lot. Upon which vehicle is the force of impact greater? Which
vehicle undergoes the greater change in acceleration? Defend your answer.
6.
What is wrong with the following statement: “Inertia is the force that keeps a moving object in motion”.
Problem Solving Practice – it is always recommended that you draw a FBD and write the ΣF equations
before attempting to do any math!
1.
A horizontal force of 30.0 N is used to slide a 12.0 kg wooden crate across the floor to the right. A 10.0 N frictional force
works against you. What is the acceleration of the crate?
2.
The maximum force a grocery sack can withstand and not rip is 250N If 20.0 kg of groceries are lifted from the floor to a
table top with a 5.00 m/s2 acceleration, will the sack hold?
3.
A force of 40.0 N accelerates a 5.0 kg block at 6.0 m/s2 to the right along a horizontal surface. How large is the frictional
force?
4.
A 4500 kg helicopter accelerates upward at 2.0 m/s2. What is the lift force exerted by the air on the propellers?
5.
A 75 kg person exerts a force of 950 N on the floor in addition to her weight in the process of jumping. What will be the
acceleration of this person as they are jumping?
6.
You pull your 18.0 kg suitcase at a constant speed across the floor by the handle which makes an angle of 51° with the
horizontal. The frictional force on the suitcase is 27.0 N.
a. How much force is being used to pull the suitcase?
b. What is the normal force on the suitcase?
c. Find the value of μ between the suitcase and the floor
7.
A 65 kg person is standing on a bathroom scale in an elevator. A scale reads the normal force between the person and
the scale. Draw a FBD for the person and determine the reading on the scale when the elevator accelerates upwards at
a rate of 2.0 m/s2.
8.
A child pushes a 18 kg wagon across level ground with a 15.0 N force downward and to the right at an angle of 20.0°
with respect to the horizontal. If the coefficient of friction between the wagon and ground is 0.10 determine the normal
force on the wagon and the acceleration of the wagon.
9.
A1100 kg car starts from rest and accelerates to a speed of 25 m/s in a time of 4.5 s. What is the net force on the car?
10. A 0.50 kg model rocket experiences a thrust force that accelerates the rocket vertically from rest to a speed of 35 m/s
over a distance of 20.0 m. What is the magnitude of the thrust?
11. A sled and rider with a combined mass of 102 kg travels down a hill at an incline of 25 degrees. The coefficient of
friction between the sled and the snow is 0.080. Find the acceleration of the sled and rider.
12. Basking in the sun, a 1.10 kg lizard lies motionless on a rock tilted at an angle of 15 degrees with respect to the
horizontal.
a.
What is the magnitude of the normal force exerted by the rock on the lizard?
b.
What is the magnitude of the frictional force exerted by the rock on the lizard?
Multiple Choice Key
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E
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C
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C
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C
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B