Calculation of torque to stop a wheel.

[cheapstrike]

Homework Statement

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

Answer - (A).

Homework Equations

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

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.

 

[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.

 

[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".

 

[cheapstrike]

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".

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

 

[cheapstrike]

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

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