A uniform meterstick of negligible thickness lies horizontally on a frictionless tabletop
PHYSICS · Multi-part · A Level · Physics · Mechanics and materials · Mechanics and materials
Problem
A uniform meterstick of negligible thickness lies horizontally on a frictionless tabletop. Two identical spring scales pull straight upward on the stick at fixed points that are 10 cm and 90 cm from the left end, respectively. The magnitudes of the pulls always remain 3.0 N and 5.0 N, respectively. The stick is lifted slightly off the table and is free to rotate about any horizontal axis that passes through the stick.
Assume the positive direction for torque is counter-clockwise when viewed from above.
(a) Describe qualitatively how the net torque on the stick changes as the pivot point is chosen successively at the 0 cm mark, the 50 cm mark, and the 100 cm mark. In your answer, indicate the direction of the net torque for each of the three pivot choices.
(b) Identify the exact pivot location(s) (if any) at which the 3.0 N pull produces zero torque. Explain why its torque vanishes at that location even though the force itself does not change.
(c) The stick is said to be in static equilibrium when the vector sum of forces is zero and the net torque about every axis is also zero. Explain whether verifying zero net torque about only one carefully chosen pivot axis is sufficient to conclude that the stick is in rotational equilibrium for this scenario.