Q: A wheel having moment of inertia 2 kg-m^2 about its vertical axis, rotates at the rate of 60 rpm about this axis. The torque which can stop the wheel’s rotation in one minute would be
(a) 2π/15 N-m
(b) π/12 N-m
(c) π/15 N-m
(d) π/18 N-m
Ans: (c)
Sol: L = I ω ; Where I = Moment of Inertia
L = I (2 π ν) ; Where ν = frequency
L = 2 (2 π × 1 ) = 4 π
Torque = L/Δt = 4π /60 = π /15 N-m