# Torque, the mass that can be lifted, and speed it rises

1. Oct 31, 2009

### katamoria

1. The problem statement, all variables and given/known data

a. compute the torque developed by an industrial motor whose output is 225kW at an angular speed of 4000rpm.
b. a drum with negligible mass and .4m diameter is attached to the motor shaft, and the power output of the motor is used to raise a weight hanging from a rope wrapped around the drum. how heavy a weight can the motor life at constant speed?
c. at what constant speed will the weight rise?

2. Relevant equations
1Kw = 3.6x10^6J
Power = (torque)(angular speed)?
V = Rw

3. The attempt at a solution
i changed the w from rpm to rad/s
I converted kW to J and got 81x10^8J
I'm not sure that's right, that seems really big to me.
and if Power = (torque)(angular velocity) then i rearranged and solved for torque and got 19.4x10^6, which seems high to me
I have no idea what to do with part B
I know that tension in the rope equals the weight of the object tied to it.