Torque Calculations: Solve for Disc Revolutions with Opposing Torque

[Kratos521]

Homework Statement

The torque is removed when the disc is rotating at 8.0 rad s-1. An opposing torque of 14.5 N m is applied to slow the disc down. Calculate the number of revolutions the disc makes after the second torque is applied, before it comes to rest.

Relevant Equations

T=Is
W=Wo +at^(2)
W^(2)=Wo^(2) +2aθ

Homework Statement: The torque is removed when the disc is rotating at 8.0 rad s-1. An opposing torque of 14.5 N m is applied to slow the disc down. Calculate the number of revolutions the disc makes after the second torque is applied, before it comes to rest.
Homework Equations: T=Is
W=Wo +at^(2)
W^(2)=Wo^(2) +2aθ

The answer is 14revs

 

[Doc Al]

Hint: What's Newton's 2nd law for rotation? (That will allow you to calculate the angular acceleration.)

 

[Kratos521]

Hi, Thank you for the reply. I know that T=Ia and that it is the sum of Torques that are used in the calculation but I still can't get the answer, can u give me a step by step guide for this question. Thx a lot.

 

[Doc Al]

Now it's your turn to take a crack at solving the problem. Find the angular acceleration, then apply your kinematic formulas. (One of those formulas is exactly what you need.)

 

[Kratos521]

I get it now thx!