PHYSICS · Single correct · A Level · Physics · Mechanics and materials · Mechanics and materials
Problem
A student asserts that, when analyzing a rigid beam that is at rest, torques must be calculated about the point where the beam is physically supported; otherwise the equilibrium condition will not be satisfied. Which of the following statements best evaluates this assertion?
(a) The assertion is correct; the net torque is zero only when calculated about the actual support point.
(b) The assertion is incorrect because changing the pivot always changes each individual torque, so the net torque cannot be zero at more than one point.
(c) The assertion is incorrect because, in rotational equilibrium, the net torque must be zero about any point that is chosen as a pivot.
(d) The assertion is correct only for beams of uniform mass distribution; non-uniform beams require a different pivot.