A flywheel initially at rest is subjected to a constant clockwise torque of magnitude…
PHYSICS · Single correct · CBSE · Physics · System of Particles and Rotational Motion · System of Particles and Rotational Motion
Problem
A flywheel initially at rest is subjected to a constant clockwise torque of magnitude τ for the first 2.0s. Immediately afterward, a constant counterclockwise torque of the same magnitude τ is applied for the next 2.0s. Neglect friction. Which statement best describes the flywheel’s angular velocity at t=4.0s?
(a) Clockwise and equal in magnitude to the angular speed it had at t=2.0s, because the counter-torque merely stops the angular acceleration, not the rotation itself.
(b) Counterclockwise and smaller—about one-half the speed it had at t=2.0s—because the opposite torque slows the flywheel but does not have enough time to stop it completely.
(c) Zero, because the equal but opposite torques act for equal time intervals, leaving no net change in angular velocity.
(d) Zero and the flywheel is back at its starting angular position, since the torques exactly cancel the entire motion.