Download WS: Friction

Unit 3 WS6: Friction
NAME___________________________ Per
Review Questions
a. What happens to an object when the net force on it is zero?
b. True or False? An object acted upon by a force of +5N and -5N will have a constant velocity.
c. Car A has an acceleration of -2 m/s/s and Car B moves with a velocity of +5m/s through out its trip.
Which of the cars has non-zero net force acting on it?
d. What is the difference between static friction and kinetic friction?
1. Calculate the coefficient of friction between a tabletop and the following three materials that move with
constant velocity parallel to the table surface.
a) Ff = 15 N, FN = 80N
b) Ff = 24N, FN = 160N
c) Ff = 15N, FN = 16N
d) Which has the biggest coefficient of friction? Describe what coefficient of friction tells you
about a pair of objects?
e) Draw fully labeled force diagrams for each of these objects.
2. Ms. Yahaya is the science consultant for Nike sports shoe department. The department wants her to
improve the coefficient of friction between hardwood floor and basketball shoes. The present mu is 0.99
when Ff =485N and FN =490N. Ms. Yahaya determines that Ff should be 510N. Find the new coefficient
of friction between a shoe of the same weight and the floor.
3. A. Which of the following graphs is correct, based on your friction experiments? Explain.
Ff
(N)
3
Ff
(N)
Ff
(N)
4
2
2
2
10
20
FN
(N)
10
15
FN
(N)
B. Do these graphs represent static or kinetic friction?
10
15
Area
(m2)
4. A 6.0 kg block is tied to a rope and pulled along a cement floor with a tension of -6N. The block moves
with constant velocity the entire time.
a. Draw a fully labeled force diagram for the object.
-6N
b. How big is the friction force on the block during this motion?
c. Calculate the coefficient of friction between the two surfaces.
5. A 500 kg car moves with a constant velocity on an icy road. The coefficient of friction between the car
tire and icy road is 0.3. How much friction force will be required to keep it from sliding?
6. A shipdocker loading crates on a ship finds that a 40Kg crate initially at rest requires a horizontal force
of 150N to set it in motion.
a. Find the coefficient of static friction between the crate and the floor.
b. If the coefficient of kinetic friction between the surface and the crate is 0.3, find the horizontal force
required to keep the crate in motion with a constant velocity.
c. Compare the size of the kinetic friction force to the size of the static friction force.
d. If the shipdocker loaded an 80 kg crate, now how much friction force would be required to keep the
crate moving at a constant velocity?
7. a. Describe the situation at the right in words. It experiences a friction
force of 9N.
F = 35 N
a
b. Draw a fully labeled force diagram for the box, and find the net force.
Net Force = _______________
700
50kg