Question

A ring of radius 7cm is rotating about the central axis perpendicular to its plane. A force acts on it, tangentially, such that it does a work of 10J in a complete rotation. Find the value of that force. `

(a) 0.5/7π N

(b) 35π N

(c) 500/7π N

(d) 0.7 N

The question was asked during an online exam.

This key question is from Dynamics of Rotational Motion about a Fixed Axis in portion System of Particles and Rotational Motion of Physics – Class 11

Answer 1

Correct answer is (c) 500/7π N

Best explanation: Let the force be ‘F’. Work done will be = Tθ,

where T is the torque &  is the angular displacement = 2π rad.

Work = Tθ = 10

∴ T(2π) = 10

∴ T = 5/π Nm.

Also, T = r*F

∴ 5/π = 0.07*F

∴ F = 500/7π N.