Name
Period
Date
Net Force (Unbalanced Forces) Review
1. Use the results of the Newton’s Second Law Lab to state the relationships between
the following variables.



 
a. a and F
b. a and m
c. a , F and m

with constant m
with constant F
d. If the mass of an object was tripled while the force was kept constant, what
would happen to the resulting acceleration? How do you know?
e. If the force acting upon an object was cut in half while the mass was kept
constant, what would happen to the resulting acceleration? How do you know?
f. If both the force and the mass were doubled, what would happen to the resulting
acceleration? How do you know?
g. If the force acting upon a mass was doubled while the mass was cut in half, what
would happen to the resulting acceleration? How do you know?
2. Consider Newton's Second Law of Motion to determine which of the following
statements are true. Circle all that apply.
a. If an object is accelerating to the right, the net force on the object must be
directed towards the right.
b. If an object is moving to the right and slowing down, then the net force on the
object is directed towards the left.
c. Accelerating objects are either slowing down or speeding up.
d. The acceleration of an object is directly dependent upon its mass and inversely
dependent upon its net force.
e. An object has an acceleration of 8 m
. If the net force acting upon the object is
s2
increased by a factor of 2, then the new acceleration would be 10 m 2 .
s
Net Force Review
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f. An object has an acceleration of 8 m
. If the net force acting upon the object is
s2
increased by a factor of 3, then the new acceleration would be 11 m 2 .
s
g. An object has an acceleration of 8 m
. If the mass of the object is increased by
s2
a factor of 2, then the new acceleration would be 16 m 2 .
s
h. An object has an acceleration of 8 m
. If the mass of the object is increased by
s2
a factor of 4, then the new acceleration would be 2 m 2 .
s
i.
An object has an acceleration of 8 m
j.
An object has an acceleration of 8 m
. If the net force acting upon the object is
s2
increased by a factor of 2 and the mass of the object is decreased by a factor of
2, then the two factors would offset each other and the acceleration would still be
8m 2 .
s
. If the net force acting upon the object is
s2
increased by a factor of 2 and the mass of the object is increased by a factor of
4, then the new acceleration would be 4 m 2 .
s
k. An object has an acceleration of 8 m
. If the net force acting upon the object is
s2
decreased by a factor of 2 and the mass of the object is increased by a factor of
4, then the new acceleration would be 1 m 2 .
s
l.
An object has an acceleration of 8 m
. If the net force acting upon the object is
s2
increased by a factor of 4 and the mass of the object is increased by a factor of
2, then the new acceleration would be 16 m 2 .
s
m. A 2 kg object accelerates from rest to a final velocity of 6 m
s
in 3 seconds. The
magnitude of the net force acting upon the object is 12 N.
n. A 10 kg object slows down from 24 m
to a final velocity of 9 m in 3 seconds. The
s
s
magnitude of the net force acting upon the object is 80 N.
Net Force Review
page 3
3. According to Newton's Third Law, in any interaction between two objects, the forces
exerted are always equal and opposite. The reason that these forces do not cancel
each other is
a. the action force acts for a longer time period.
b. the two forces are not always in the same direction.
c. one of the two forces is greater than the other.
d. the two forces act upon different objects; only forces on the same object can
balance each other.
e. ... nonsense! They do cancel each other. Objects accelerate because of the
presence of a third force.
4. a. Suppose you run into a stationary truck with 450 N of force. With what force
does the truck push back on you?
b. According to Greek mythology, Sisyphus was a Corinthian King condemned
forever to roll a huge rock up a hill in Hades only to have it roll back down on
nearing the top. If Sisyphus accelerated the rock up the hill with a force of
500. N , with what force and in what direction does the rock push on him?
5. As you sit in your chair and study your physics (presuming that you do), the force of
gravity acts downward upon your body. The Newton’s Third Law pair to the force of
the Earth pulling you downward is
a. the force of the chair pushing you upward.
b. the force of the floor pushing your chair upward.
c. the force of the Earth pushing you upward.
d. the force of air molecules pushing you upwards.
e. the force of your body pulling the Earth upwards.
f. ... nonsense! Gravity is a field force and there is no such reaction force.
6. A golf pro places a ball at rest on the tee, lines up his shot, draws back his club, and
lets one rip. During the contact of the golf club with the golf ball, the force of the
club on the ball is ____ the force of the ball on the club and the acceleration of the
club is ____ than the acceleration of the ball.
a. greater than, greater than
b. greater than, equal to c. greater than, less than
d. less than, less than
e. less than, equal to
g. equal to, equal to
h. equal to, greater than i. equal to, less than
f. less than, greater than
Net Force Review
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7. A 12000. kg bus slows from 30. m
to 10. m in 10. s .
s
s
a. What is the acceleration of the bus? b. What is the net force acting on the bus?
8. A 75 kg man stands on a scale in an elevator that slows from  6.0 m
a. Draw a force
diagram of the man.
b. Calculate his
acceleration.
to rest in 2.0 s .
s
c. Write a net force
equation of the vertical
forces and then calculate
the scale reading as he
accelerates.
100. N
10. kg
30.
9. A 10. kg box is dragged across a frictionless horizontal surface by a 100. N force
that is applied at a 30. angle from the horizontal as in the diagram above.
a. Draw a force diagram of the box.
b. Write a net force equation of the
horizontal force(s) acting on the box
and then calculate its acceleration.
10. kg
c. Write an equation for the three vertical forces acting on the box and then
calculate the normal force.
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200. N

FA

10. You pull on a 200. N box with a horizontal force FA that is just enough force to get it
to move at constant velocity. The coefficient of static friction between the box and
the ground is  s  0.60 while the coefficient of kinetic friction is  k  0.45
a. Draw a force
diagram of the box.
b. Calculate the force of
c. With what force would
kinetic friction acting
you need to pull the box
between the box and the
in order for it to move at
floor.
constant velocity?
200. N
Now you pull on the box horizontally with a force of 125 N .
d. Draw a new force diagram of the
box.
e. Write a net force equation of the
horizontal forces and then calculate the
resulting acceleration.
200. N
f. What is the smallest force with which you could pull horizontally on the box and
get it to move? Begin by drawing a force diagram of the box.
Net Force Review
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5.0 kg
35
11. A 5.0 kg box rests upon a frictionless 35 incline as shown.
a. Draw a force diagram of the box.
b. Write an equation of the
perpendicular forces and then
calculate the normal force acting on
the box.
5.0 kg
c. Write a net force equation of the parallel force(s) and then calculate the resulting
acceleration of the box.