Examples Answers
1. Can you have an an object that is not in equilibrium but the net forces on it are zero?
2. When you carry a heavy load in your arms, you lean backwards to maintain balance. Why?
3. What condition or conditions are necessary for rotational equilibrium?
a. åFx = 0
b. åFx = 0, åt = 0
c. åt = 0
d. åFx = 0, åFy = 0
4. A book weights 8 N. When held at rest 6 inches above your head the net force on the book is
a. 0 N
b. 6 N
c. 8 N
d. -6 N
e. -8 N
5. A sphere hanging freely from a cord is in
a. Stable equilibrium
b. Static equilibrium
c. Unstable equilibrium
d. Neutral equilibrium
e. Positive equilibrium
6. A cube resting on a horizontal table top is in
a. Stable equilibrium
b. Static equilibrium
c. Unstable equilibrium
d. Neutral equilibrium
e. Positive equilibrium
7. A child at the top of a sliding board is in
a. Stable equilibrium
b. Static equilibrium
c. Unstable equilibrium
d. Neutral equilibrium
e. Positive equilibrium
8. A 15.0 kg person (person 1) holds on to a rope attached to a tree. Person 2 applies a horizontal force and pulls person 1 back a certain
distance before releasing. The rope makes an angle of 37.0 degrees with the vertical. What is the magnitude of the force exerted by
person 2?
9. Assume that the two wheels shown below are mounted on the same axle and move together. The radii of the wheels are given, along with
the mass of the object on the right. Does this arrangement give a mechanical advantage? Why?
Study the following examples from the text
10. Example 9-2: Chandelier cord tension.
11. Example 9-3: Multiplying force using a lever
12. Example 9-4: A seesaw in equilibrium:
13. Example 9-5: Forces on a beam and support - note the convenient choice of the axis for the torque equation
14. Example 9-6: Hinged beam and cable - note the convenient choice of the axis for the torque equation