Name
Period
Date
Net Force Worksheet 6: Friction
1. A classroom desk supported by long legs is stationary in the room. A teacher
comes around and pushes upon the desk in an effort to start it into a state of
motion. The desk does not budge. The desk remains at rest because ______.
a. there is a force of static friction opposing its motion
b. there is a force of kinetic or sliding friction opposing its motion
c. there is a force of rolling friction opposing its motion
d. there are small dust mites at the desk's feet that push back on the desk to keep
it at rest
2. A classroom desk supported by long legs is stationary in the room. A teacher
comes around and pushes upon the desk in an effort to start it into a state of
motion. The desk is finally accelerated from rest and then moves at a constant
speed of 0.5 m . The desk maintains this constant speed because ______.
s
a. there is a force of static friction balancing the teacher's forward push
b. there is a force of kinetic or sliding friction balancing the teacher's forward push
c. there is a force of rolling friction balancing the teacher's forward push
d. the teacher must have stopped pushing
3. The symbol  stands for the _____
a. coefficient of friction
b. force of friction
4. The units on  are _____
a. Newton
b. kg
c. m/s/s
c. normal force
d. ... nonsense! There are no units on  .
5. You are walking down the hallway to the right at a constant velocity. Being a
thoughtful physics student you wish to analyze the forces that allow you to walk.
What direction(s) do you push on the floor in order to walk to the right at constant
velocity?
a.
Down only
b.
Down
and
left
c.
Down
and
right
d.
Nonsense, I don’t push on the floor at all!
6. Given your understanding of Newton’s 3rd Law, if you push on the floor, what does
the floor do to you?
a. Nothing, the floor is an inanimate object and therefore cannot apply a force!
b. The floor pulls on you.
c. The floor pushes on you.
d. Since I answered (d) to #5, I must believe that I don’t interact with the floor at all
as I walk!
Net Force Worksheet 6
page 2
7. What direction(s) does the floor push on you as you walk to the right at a constant
velocity?
a.
Up only
b.
Up
and
right
c.
Up
and
left
d. Nonsense, I don’t push on the floor at all! That’s my answer and I’m sticking to it!
8. What kind of benevolent force is it then that pushes you to the right and allows you
to walk?
a. Friction
b. Normal
c. Gravity
d. I keep telling you, I don’t interact with the floor when I walk, so no force pushes
me forward when I walk.
9. Given your hopefully correct answers to #5 – 8, if you wanted to walk faster what
should you do and why?







10. Use the friction equation F f  FN and Newton’s 2nd Law Fnet  ma to fill in the
blanks in the following situations. Use g  10 N
kg
if needed.
Net Force Worksheet 6
page 3
11. A block weighing 300. N is moved at constant speed over
a horizontal surface by a force of 50. N applied parallel to
the surface.
a. Draw a force
diagram for the
block.
b. Write an equation for
the horizontal forces
acting on the box.
Calculate the amount of
kinetic friction acting on
the box.
300. N
50. N
c. Write an equation for
the vertical forces acting
on the box. Calculate
the normal force acting
on the box.
300. N
d. What is the coefficient of kinetic
friction (  k )?
e. Assume the surface is frictionless
 k  0 . Draw a new force diagram.
Write a net force equation for the
horizontal forces and then calculate the
resulting acceleration of the box
300. N
Net Force Worksheet 6
page 4
100. N
50. kg
 k  0.15
12. A 100. N force is applied to a 50. kg crate moving on a level floor. The coefficient of
kinetic friction between the crate and the floor is 0.15 .
a. Draw a force
b. Write an equation for
c. What is the force of
diagram for the
the vertical forces
kinetic friction acting on
crate.
acting on the box.
the box?
Calculate the normal
force acting on the box.
50. kg
d. Write a net force equation for the horizontal forces. What is the acceleration of
the crate?
13. Suppose that in the situation described in question 12, the crate begins at rest and
the coefficient of static friction is  s  0.25 .
b. Draw a force diagram for the crate in
a. Is the 100. N force sufficient to
this situation. How much static friction
cause the crate to begin moving?
actually acts in this case? How do you
Calculate the maximum force of
know?
static friction and compare.
50. kg