Question

A solid disk with a radius of `6 m` and mass of `8 kg` is rotating on a frictionless surface. If `3 W` of power is used to increase the disk's rate of rotation, what torque is applied when the disk is rotating at `5 Hz`?

Answer 1

`tau=(3" W")/(10pi)~~9.55N*m`

Explanation:

We are told we have a rotating spinning coin.

http://www.mariowiki.com/coin

Step 1. Gather the information that you know and need

• Mass of disk: `"mass"=m=8" kg"`
• Radius of disk: `"radius"=r=6" m"`
• Power applied to increase rotation: `P=3" W"`
• Frequency: `f=5" Hz"`
• Torque required: ??

Step 2. Determine the formula using the above givens

• `P` is the power applied, `P=tau omega`
• Therefore, the formula for torque is `tau=P"/"omega`
• Angular speed, `omega=f*2pi=5*2pi=10pi`

Step 3. Plug your answer into the formula for torque

`tau=(3" W")/(10pi)~~9.55N*m`