Name
Period
Date
Net Force (Balanced Forces) Worksheet 8
M
M
System A
System B
M
M
System C
M
M
M
M
1. The three modified Atwood's machines shown above have blocks of mass M on a
frictionless surface and also hanging from a string. When the blocks are released,
they accelerate as they did in our lab.
a. Which system has the greatest net b. Which system has the least inertia?
force? Explain how you know.
Explain how you know.
c. Determine the acceleration for each system.
A
B
B
A
2. A 20. kg block (A) rests on a frictionless table; a cord attached to the block extends
horizontally to a pulley at the edge of the table. 10. kg of mass (B) hangs at the end
of the cord.
a. Draw a force diagram of the situation on the diagram above using as your
system the block and the mass together.
b. Write a net force equation for the horizontal forces acting on the system and
then calculate the acceleration of the block and mass system.
Net Force Worksheet 8
page 2
c. Clearly draw and label the forces acting on each object (2 force diagrams).
A
B
d. Write a net force equation for the
e. Write a net force equation for the
horizontal forces acting on block A
vertical forces acting on mass B and
and then calculate the tension in the
then calculate the tension in the cord.
cord.
3. Below is a picture of an Atwood's Machine: two masses attached to a frictionless,
massless pulley (pretty neat how physicists dream up equipment like this, huh?).
The mass of block A is 5.0 kg, and the mass of B is 2.0 kg.
a. Draw a force diagram of the system.
B
B
A
A
b. Write a net force equation for the
vertical forces acting on the system
and then calculate the acceleration
of the system when the blocks are
released.
c. How long will it take for block A to fall
2.0 m?
Net Force Worksheet 8
4.0 kg
A
page 3
A
1.0 kg
B
B
4. Suppose a hanging 1.0 kg lab mass is attached to a 4.0 kg block on the table. The
coefficient of kinetic friction between the block and the table is 0.20 . Draw a force
diagram for the system on the diagram above right.
a. Write an equation for the vertical
forces acting on the system. What
normal force is acting on the system?
b. Calculate the force of kinetic friction
acting on the system.
c. Write a net force equation for the horizontal forces acting on the system. What is
the acceleration of the block?
d. What is the minimum value of the coefficient of static friction  s  in order for the
block to remain motionless?
Draw a new force diagram of the system in this situation on the diagram below.
Write an equation for the horizontal forces acting on the system and then answer
the question.
B
A