Question

A disc is under pure rolling motion on a horizontal surface. The speed of the topmost point at an instant is 5m/s w.r.t the centre of the disc. What is the velocity of the centremost point? The radius of the disc is 10cm.

(a) 5m/s

(b) 0m/s

(c) 2.5m/s

(d) 2m/s

The question was posed to me in an interview for job.

The above asked question is from Rolling Motion in chapter System of Particles and Rotational Motion of Physics – Class 11

Answer 1

The correct choice is (a) 5m/s

To elaborate: The speed of any point w.r.t the centre is equal to R⍵,

where ‘ω’ is the angular speed & ‘R’ is the distance of that point from the centre.

In pure rolling motion, we know that V = Rω,

where V is the velocity of centre of mass.

∴ The velocity of centre of mass = 5m/s, since Rω = 5.