A circular disc is rotating about a central axis perpendicular to its diameter with a speed of 5rad/s. If a constant force of 2N is applied tangentially on it, in how much time will it come to a stop? Radius of disc = 1m & mass = 1kg.(a) 0.257s(b) 5s(c) 1.25s(d) 2.5sThe question was asked during an interview.Query is from Kinematics of Rotational Motion about a Fixed Axis topic in section System of Particles and Rotational Motion of Physics – Class 11

A circular disc is rotating about a central axis perpendicular to its

1.	A circular disc is rotating about a central axis perpendicular to its diameter with a speed of 5rad/s. If a constant force of 2N is applied tangentially on it, in how much time will it come to a stop? Radius of disc = 1m & mass = 1kg.(a) 0.257s(b) 5s(c) 1.25s(d) 2.5sThe question was asked during an interview.Query is from Kinematics of Rotational Motion about a Fixed Axis topic in section System of Particles and Rotational Motion of Physics – Class 11
Answer» Correct option is (c) 1.25s For explanation: Let R be the radius, I be the MOMENT of inertia, a be the angular ACCELERATION & F be the FORCE applied.Moment of inertia of disc about given axis = MR^2/2 = 0.5 kgm^2.Torque = r X F = 2Nm. But, torque is also = Ia.∴ a = 2/0.5 = 4 rads^2.Using, w = w0 + a*DT, we get:0 = 5 – 4dt, where dt is the time interval. ∴ dt = 5/4 = 1.25s.

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