Which of the following are correct expressions for torque acting on a body? A. τ = r×L. B. τ = d(r×p)/dt. C. τ = r×(dp/dt). D. τ = Iα. E. τ = r×F. Choose the correct set.
Options

Question

Which of the following are correct expressions for torque acting on a body? A. τ = r×L. B. τ = d(r×p)/dt. C. τ = r×(dp/dt). D. τ = Iα. E. τ = r×F. Choose the correct set.

G1 Physics · Accepted Answer

Angular momentum of a particle is L = r×p. Torque is the rate of change of angular momentum: τ = dL/dt = d(r×p)/dt. Therefore B is correct. Also, dp/dt = F, so r×(dp/dt) = r×F = τ. Hence C and E are correct. For a rigid body rotating about a fixed axis with constant moment of inertia, τ = Iα, so D is correct. Expression A, τ = r×L, is not the definition of torque and is dimensionally incorrect. Thus B, C, D and E are correct. Correct option: D.