Name _____ KEY ____________________________________ Date _________ Period ______
Net Forces
Sketch free body diagrams for the following situations. Include symbols such as: Fa, W, Fn, Fk, Fs,
Fair, Ft, Fspring. Include the amount of force in the diagrams.
1.
A 4.55 kg book is at rest on a table:
Fn = 44.6 N
a. Draw the free-body diagram to the right.
Book
b. Is there a net force on the book? Explain.

2.
Fg = 44.6 N
Because the forces are balanced up and down,
there is no net force.
A 35 kg dog in free fall that experiences 300. N of air resistance.
a. Draw the free-body diagram to the right.
Fair = 300. N
b. Calculate the net force on the dog. Include direction.
Dog

3.
Fnet = Fg – Fair = 343 N – 300. N = 43 N down
Fg = 343 N
A 400. kg car whose engine applies a force of 1200. N to accelerate
leftward. The car experiences a 200. N frictional force.
a. Draw the free-body diagram to the right.
Fa = 1200. N
Fn = 3920 N
Car
b. Calculate the net force on the car. Include direction.

4.
Fg = 3920 N
Fnet = Fa – Ff = 1200. N – 200. N = 1000. N left
Fair = 20. N
A 2.04 kg cat in free fall experiences 20.0 N of air resistance.
a. Draw the free-body diagram to the right.
b. Calculate the net force on the cat. Include direction.

The net force is 0, because the forces are
balanced.
c. Is the cat accelerating or moving with constant speed?
Explain.

Ff = 200. N
The car is moving at constant speed because of
Newton’s 1st law (inertia).
Cat
Fg = 20. N