A disc is standing on a flat rough surface. Its centre is suddenly given a velocity of 5m/s in the forward direction. In how much time will pure rolling start? Mass = 1kg, Radius = 10cm. Coefficient of friction = 0.4.(a) 0.25 s(b) 0.05 s(c) 0.5 s(d) 1 sI got this question in an interview.My enquiry is from Rolling Motion in portion System of Particles and Rotational Motion of Physics – Class 11

A disc is standing on a flat rough surface. Its centre is suddenly giv

1.	A disc is standing on a flat rough surface. Its centre is suddenly given a velocity of 5m/s in the forward direction. In how much time will pure rolling start? Mass = 1kg, Radius = 10cm. Coefficient of friction = 0.4.(a) 0.25 s(b) 0.05 s(c) 0.5 s(d) 1 sI got this question in an interview.My enquiry is from Rolling Motion in portion System of Particles and Rotational Motion of Physics – Class 11
Answer» Right choice is (a) 0.25 s Easy explanation: Friction force will DECREASE its linear velocity & increase its ANGULAR velocity. F = Ma .Friction ‘f’ = μN = 0.4110 = 4N. Thus, v = v0 – at&w = w0 + (a/R)t. For pure rolling v = wR, thus: v0 – at = R(w0 + (a/R)t).a = f/M∴ 5 – 4/1 = 0.1(0 + (4/0.1)t) ∴ 10 = 40t OR t = 0.25 s.

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