Paper Details

A box full of books rests on a wooden floor. The normal force the floor exerts on the box is 250 N.

(a) You push horizontally on the box with a force of 120 N, but it refuses to budge. What can you say about the coefficient of static friction between the box and the floor?

(b) If you must push horizontally on the box with a force of at least 150 N to start it sliding, what is the coefficient of static friction?

(c) Once the box is sliding, you only have to push with a force of 120 N to keep it sliding.

What is the coefficient of kinetic friction?

Consider a pendulum made of a massless rod of length ? and a point mass m. Assume conditions have been set up so that the mass moves in a horizontal circle. Let ? be the constant angle the rod makes with the vertical. Find the frequency, ?, of this circular motion in three different ways.

(a) Use F = ma. (The net force accounts for the centripetal acceleration.)22

(b) Use ? = dL/dt with the pendulum pivot as the origin.

(c) Use ? = dL/dt with the mass as the origin.