You have been asked to demonstrate the power of electric forces to a class of fifth
graders. For the demonstration, you charge a
balloon by rubbing it with animal fur. Then
you hold the balloon a few centimeters above
the head of a student with long hair.
1. Describe what will happen to the student's
hair as you bring the balloon closer and closer
to it.

Two steel balls, each of mass m, are welded to a light rod of length l and negligible mass and are initially at rest on a smooth horizontal surface. a horizontal force of magnitude f is suddenly applied to the rod as shown. determine (a) the instantaneous acceleration a of the mass center g and (b) the corresponding rate at which the angular velocity of the assembly about g is changing with time.