# A solid disk with a radius of #9 m# and mass of #2 kg# is rotating on a frictionless surface. If #480 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#?

##### 1 Answer

Feb 9, 2017

#### Explanation:

We are told we have a rotating spinning coin.

Step 1. Gather the information that you know and need

- Mass of disk:
#"mass"=m=2" kg"# - Radius of disk:
#"radius"=r=9" m"# - Power applied to increase rotation:
#P=480" 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, torque is
#tau=P"/"omega# - Angular speed,
#omega=f*2pi=5*2pi=10pi#

Step 3. Plug your knows into the formula for torque