1. Which of the following is not an example of friction? a. Air resistance. c. a desk at rest.
b. a ball rolling down a hill. d. getting warm by a campfire.
2. Which is an example of helpful friction?
a. getting a static shock c. sliding across a gym floor on your
b. wearing batting gloves d. All of the above
3. The gravitational force between two objects depends on masses of objects and
a. accelerations of objects. c. speeds of objects.
b. distance between objects. d. sizes of objects.
4. Which of the following objects exerts the largest gravitational force?
a. a 10 kg bowling ball c. a 0.2 kg feather
b. a 1kg book d. All are the same

Dinate system, and a charge q = - 2.00 nc is placed s2 10 n> c. (a) what is the change in electric potential energy when the dipole moment of a molecule changes its orientation with respect to es from parallel to perpendicular? (b) at what absolute temperature t is the average translational kinetic energy 32 kt of a molecule equal to the change in potential energy calculated in part(: abovethistemperature,thermalagitationprevents the dipoles from aligning with the electric field.) placed in a uniform electric field e with magnitude 1.6 * 6 on the positive x-axis at x = 4.00 cm. (a) if a third charge q3 = +6.00 nc is now placed at the point x = 4.00 cm, y = 3.00 cm, find the x- and y-components of the total force exerted on this charge by the other two. (b) find the magnitude and direction of figure p21.62 ll uu 21.55 . torque on a dipole. an electric dipole with dipole moment ps is in a uniform external electric field es. (a) find the orientations of the dipole for which the torque on the dipole is zero. (b) which of the orientations in part (a) is stable, and which is unstable? (hint: consider a small rotation away from the equi- librium position and see what happens.) (c) show that for the stable orientation in part (b), the dipole’s own electric field tends to oppose the external field. 21.62 ..