Name
Period
Date
Net Force (Unbalanced Forces) Worksheet 4
1. A 4600 kg helicopter accelerates upward at 2.0 m 2 . The force of the air on the
s

propellers is called a lift force FL .
a. Draw a force
b. Write a net force
c. What lift force is exerted
diagram of the
equation for the vertical
by the air on the
helicopter. (Which
forces acting on the
propellers?
force is bigger?
helicopter.
How do you know?)
 
2. The maximum force that a grocery bag can withstand without ripping is 250 N .
Suppose that the bag is filled with 20. kg of groceries and lifted with an acceleration
of 5.0 m 2 .
s
a. Draw a force
b. Write a net force
c. Do the groceries stay in
diagram of the
equation for the vertical
the bag?
groceries. (Which
forces acting on the
force is bigger?
groceries.
How do you know?)
3. A sign in an elevator states that the maximum occupancy is 20. persons . Suppose
that the safety engineers assume the mass of the average rider is 75 kg . The
elevator itself has a mass of 500. kg . The cable supporting the elevator can tolerate
a maximum force of 30 000. N .
a. Draw a force
b. Write a net force
c. What is the greatest
diagram of the
equation for the vertical
acceleration that the
elevator. (Which
forces acting on the
elevator's motor can produce
force is bigger?
elevator.
without snapping the cable?
How do you know?)
Net Force (Unbalanced Forces) Worksheet 4
page 2
Problems #4 – 7 require you to use the kinematic equations as well as Newton's
2nd Law. The variable that ties both the kinematic equations and Newton’s 2 nd Law
together is acceleration. Depending on the variables you know, use either the net
force equation or the kinematic equations to solve for acceleration, and then use the
acceleration value to solve for the unknown quantity. Remember, the kinematic
equations are
  
v  vo  at
1  
 
x  x0  v  v o t
2
1
 

x  xo  vo t  at 2
2
2 2
  
v  v o  2a  x  x o 
4. A race car has a mass of 710 kg . It starts from rest and travels 40.0 m in 3.0 s . The
car is uniformly accelerated during the entire time.
a. What is the car’s acceleration?
b. What net force is acting on the car?
c. Draw a force diagram for the car. It
will have a forward applied force
from the road and a force of
friction/drag opposing its motion.
d. Write the net force equation for the
horizontal forces. If the total frictional
force acting on the car is 1500. N, what
applied force is acting on the car?
5. Suppose that a 1000. kg car is traveling at 25.0 m
a force of 5000. N .
a. Draw a force
diagram of the car
as it slows to a stop.
s
 55mph when its brakes apply
b. Write the net force
equation for the axis
along which the forces
are not balanced, and
then calculate the
acceleration of the car.
c. What is the minimum
distance required for
the car to stop?
Net Force (Unbalanced Forces) Worksheet 4
page 3
6. A 900. kg car exerts 5000. N of force on a level road while being opposed by 1000. N
of friction and drag forces combined.
a. Draw a force
b. Write the net force
c. If the car starts from
diagram for the car.
equation for the axis
rest, how long will it take
along which the forces
it to accelerate to
are not balanced and
26.8 m  60 mi ?
h
s
then calculate the
acceleration of the car.


7. During a head-on collision, a passenger in the front seat of a car accelerates from
13.3 m  30mph to rest in 0.100 s .
s
a. What is the
b. Draw a force
c. The driver of the car holds out his
acceleration of
diagram of the
arm trying to keep his 25.0 kg
the passenger?
passenger.
child (who is not wearing a seat
belt) from smashing into the
dashboard. What force must he
exert on the child?
d. What is the weight of the child?
e. Convert the forces in (c) and (d) from
 1 lb. 
N to lbs.  
 . What are the
 4.45 N 
chances the driver will be able to stop
the child?