# Flywheels' torque & power

1. May 11, 2010

### ZzZerozZ

1. The problem statement, all variables and given/known data
Flywheels are large, massive wheels used to store energy. They can be spun up slowly, then the wheel's energy can be released quickly to accomplish a task that demands high power. An industrial flywheel has a 1.5m diameter and a mass of 270kg . Its maximum angular velocity is 1200rmp .

a)A motor spins up the flywheel with a constant torque of 53Nm . How long does it take the flywheel to reach top speed?
Ans:180s

b) How much energy is stored in the flywheel?
Ans:6*10^5 J

c) The flywheel is disconnected from the motor and connected to a machine to which it will deliver energy. Half the energy stored in the flywheel is delivered in 2.5s . What is the average power delivered to the machine?

Ans:120000Watt

MY QUESTION IS:
d)How much torque does the flywheel exert on the machine?

2. Relevant equations
k=0.5*Iw^2
torque=F*r=Ialpha
P=F*v

3. The attempt at a solution

I try to solve with 2.5x120000= 0.5*Iw^2 then use w to find alpha and finally solve for the
Torque, but my answer is wrong.... Can anyone gve me a hint??

2. May 11, 2010

Help!!