Calculating Torque and Work: Flywheel Mass, Radius, and Time Interval

[Jtappan]

Homework Statement

A flywheel of mass 181 kg has an effective radius of 0.63 m (assume the mass is concentrated along a circumference located at the effective radius of the flywheel).

(a) What torque is required to bring this wheel from rest to a speed of 118 rpm in a time interval of 29.4 s?
_____ N·m

(b) How much work is done during the 29.4 s?
______ kJ

Homework Equations

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The Attempt at a Solution

How is this problem done when time is involved?? I am confused.

I have done I = mr^2 and that's it.

 

[dvdqnoc]

they give you 118 rpm. You have to convert that to angular velocity using factor label.

You have time and final angular velocity, so you can find angular acc. using Vf = Vi + at where Vf=final angular vel, Vi = initial angular vel (which is 0 in this case), a=angular acc, and t=time.

then just use your I = mr^2, but remember that T=Ia (torque = I * alpha) and remember that torque=F*d.

Good luck!

 

[Snoop06]

Bump...I am working on a similar problem and having trouble with part b. I have found the torque and I thought to find work I could use w=td where t is torque and d is rotational distance. What am I missing?

 

[dvdqnoc]

Work is the change in kinetic energy. KEf - KEi, but since its at rest in the beginning, its KEf - 0, which is just w=KEf. Remember to consider rotational kinetic energy, because it is rotating. Good luck to you both!