Name
Period
Date
Rotation: Worksheet 3
More Torque and Static Equilibrium
1. Three forces act tangent to a wheel about the axle labeled
“O” which is perpendicular to the page and where a = 10.0 cm
and b = 25.0 cm.
a. Compare the magnitudes of the
three torques. Justify your answer.
b. Calculate
the net torque on the wheel shown.
What direction will the wheel rotate?
2. A man applies a force of 300. N at an angle of 60.° to the door 2.00 m from the
hinges. Find the torque on the door, choosing the hinges as the point of rotation.
3. A simple pendulum consists of a small pendulum bob of mass 3.0 kg hanging at the
end of a 2.0 m long light string that is connected to a pivot point. Calculate the
magnitude of the torque (due to the force of gravity) about this pivot point when the
string makes a 25° angle with the vertical. Start by drawing a force diagram of the
pendulum bob when at 25°.
Rotation: Worksheet 3
page 2
4. A beam of mass m and length L can rotate around an axis at C.
Three forces act on the beam as shown in the diagram.
a. Compare the magnitudes of the three torques about point C.
Justify your answer.
Calculate the net torque (magnitude and direction) on the beam about
b. an axis through O perpendicular to the page and
c. an axis through C perpendicular to the page.
For each of following problems,
 Draw an extended force diagram of the object in question.
 Complete the torque bar graph quantitatively. Be sure to show all possible
torques, even if the force exerts no torque around the chosen axis of rotation,
and show the net torque acting on the object.
 Complete the additional questions.
5. A uniform metal meterstick is balanced as shown
in the figure to the right with a 1.0 kg rock attached
to the left end of the stick. (Pay attention to the
scale of the diagram). What is the mass of the
meterstick?
 net
0
Rotation: Worksheet 3
page 3
Static Equilibrium Hint:
In all of the static equilibrium problems we have examined the axis of rotation is stated. For example,
the hinge in #2 or the pivot point of the pendulum in #3. Here’s a cool thing about static equilibrium,
since the entire object is in static equilibrium, you can sum the torques around any point you choose and
the net torque must still be zero! In other words, you can choose an axis of rotation.
How does this help? In some problems, not all forces are given. Since forces that act through the axis
of rotation exert no torques, if you choose the right axis, you can eliminate any force from the problem!
6. A 350.0 N boy and a 550.0 N girl sit on a 150.0 N porch swing that is 2.0 m long. The
swing is supported by a chain on each end and the boy sits 0.50 m from the left end
and the girl sits 0.25 m from the right end.
a. Draw an extended force diagram of b. Complete the torque bar graph
the swing.
quantitatively around a point at the left
chain. Then calculate the tension in the
right chain.
 net
0
 net
c. Complete the torque bar graph
quantitatively around a point at the right
chain. Then calculate the tension in the
left chain. You should not need to use
your answer to (b).
0
Rotation: Worksheet 3
page 4
60.°
30.°
Physics
is
Phun!
1.0
m
7. A 30. kg sign is hung from two ropes as in the diagram.
a. Draw an extended force diagram of b. Complete the torque bar graph
the sign.
quantitatively around a point at the left
rope. Then calculate the tension in the
right rope.
 net
Physics
is
Phun!
0
c. Complete the torque bar graph
quantitatively around a point at the right
rope. Then calculate the tension in the
left rope. You should not need to use
your answer to (b).
 net
0