A60-kg woman stands on the very end of a uniform board, which is supported one-quarter of the way from one end and is balanced. what is the mass of the board?

a. 60 kg
b. 30 kg
c. 20 kg
d. 15 kg
e. 120 kg

Which body is in equilibrium? (1) a satellite orbiting earth in a circular orbit (2) a ball falling freely toward the surface of earth (3) a car moving with a constant speed along a straight, level road (4) a projectile at the highest point in its trajectory