JEE Main201910 Apr 2019Evening ShiftPhysicsRotational MotionActual
A metal coin of mass 5 g and radius 1 c m is fixed to a thin stick A B of negligible mass as shown in the figure. The system is initially at rest. The constant torque, that will make the system rotate about A B at 25 rotations per second in 5 s , is close to:
Options
- A1.6 × 10 - 5 N m
- B2.0 × 10 - 5 N m
- C7.9 × 10 - 6 N m
- D4.0 × 10 - 6 N m
Correct answer
B. 2.0 × 10 - 5 N m
Step-by-step solution
As torque τ is constant. ω = τ I t τ = ω I t = 2 π n × 5 4 m r 2 t = 2 π × 25 × 5 4 × 5 × 10 - 3 × 1 × 10 - 2 2 5 = 196 × 10 - 7 ≈ 2 ⋅ 0 × 10 - 5 N m