# A solid disk with a radius of #5 m# and mass of #4 kg# is rotating on a frictionless surface. If #15 W# of power is used to increase the disk's rate of rotation, what torque is applied when the disk is rotating at #4 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=4" kg"# - Radius of disk:
#"radius"=r=5" m"# - Power applied to increase rotation:
#P=15" W"# - Frequency:
#f=4" 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=4*2pi=8pi#

Step 3. Plug your answer into the formula for torque