A 1-kg rock is suspended from the tip of a horizontal meterstick at the 0-cm mark so that the meterstick barely balances like a seesaw when its fulcrum is at the 25-cm mark. From this information, the mass of the meterstick is
A)1/4 kg.
B)1/2 kg.
C)3/4 kg.
D)1 kg.
E)none of the above

Question

Quizplus · Accepted Answer

The meterstick balances when the fulcrum is at the 25-cm mark, with a 1-kg rock suspended at the 0-cm mark. This means the torque produced by the rock is balanced by the torque produced by the meterstick's own weight. Since the rock is 25 cm from the fulcrum and the meterstick's center of mass (assuming it's uniform) would be at the 50-cm mark, or 25 cm from the fulcrum on the other side, the weights must be equal for balance. Therefore, the meterstick also has a mass of 1 kg.

A 1-Kg Rock Is Suspended from the Tip of a Horizontal