(adsbygoogle = window.adsbygoogle || []).push({}); 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 4260 RPM. (b) A drum with negligible mass, 0.660 m in diameter, is attached to the motor shaft and the power output of the motor is used to raise the weight hanging from the drum. How heavy can the motor lift at a constant speed? (c) At what constant speed will the weight rise?

3. The attempt at a solution

[tex]\omega = 4260 rev/min * \frac{2\pi}{60} = 446 rad/s[/tex]

(a)[tex]P = \tau\omega[/tex]

[tex]\tau = \frac{P}{\omega} = \frac{225000}{446} = 504 Nm[/tex]

(b) This is where I got confused. I'm not sure how to figure this out. The only thing I could think of was [tex]v = r\omega = (0.660 m)(446 rad/s) = 294 m/s[/tex]. But that doesn't answer the question. Any help would be greatly appreciated.

*EDIT* I thought of something:

[tex]\tau = Fl[/tex]

[tex]F = \frac{\tau}{l} = \frac{504 Nm}{0.660 m} = 764N[/tex]

[tex]m = 764 / 9.81 = 77.9 kg[/tex]

77.9 kg moving at 294 m/s.. that sounds incredibly wrong.

I think I'm going about this wrong. Putting a max weight on motor would use up a lot of the power, so it would go really slow, if not just be able to keep the weight from falling. I really don't understand this one at all.

**Physics Forums | Science Articles, Homework Help, Discussion**

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Torque and Power (looks pretty simple)

**Physics Forums | Science Articles, Homework Help, Discussion**