Calculation of torque to stop a wheel.

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1. Jan 3, 2017

cheapstrike

1. The problem statement, all variables and given/known data

A wheel of moment of inertia 5×10-3kg-m2 is making 20 rev/s. Find the torque required to stop it in 10s is

(A) 2π×10-2Nm (B) 2π×102Nm

(C) 4π×10-2Nm (D) 4π×102Nm

2. Relevant equations

ω=2πƒ (ƒ=frequency)
Power (P) = Γω.
P = W/t.
W = ΔK.E. = (1/2)Iω2.

3. The attempt at a solution

The power delivered is equal to the rate of doing work which is equal to the change in rotational kinetic energy.
On calculating, I get the final answer as 10-2πN.m. Kindly help.

2. Jan 3, 2017

Mastermind01

You are thinking in a very complicated way! Keep it simple! Use the rotational kinematic equations and the relation between torque and angular acceleration.

3. Jan 3, 2017

CWatters

Show your working. Note that the power isn't constant. Power = torque * angular velocity
And the angular velocity is reducing.

PS My internet connection is currently unreliable so sorry in advance if I "dissapear".

4. Jan 3, 2017

cheapstrike

Oh yes. The angular velocity isn't constant. I didn't pay attention to that. Thanks.

5. Jan 3, 2017

cheapstrike

Yeah! Turns out this was a simple question. Thanks a lot!