A 30-cm diameter circular saw blade has a mass of 0.9 kg distributed uniformly in a disc.(adsbygoogle = window.adsbygoogle || []).push({});

(a) What is its rotational kinetic energy when it is operating at 4000 rpm?

(b) What average power must be applied to bring the blade from rest to its operating 4000 rpm?

Just making sure I'm doing this right...

a. Inertia=(1/2)mr^2

I=(1/2)(.9)(.15)^2

I=.0101

w=418.88

K=(1/2)Iw^2

K=(1/2)(.0101)(418.88)^2

K=886.08

b. P=average force

torque=r*F

torque=I*ang (ang being angular velocity)

so:

I*ang=r*f

F=I*ang/r

ergh...now i come to a block!!

I don't know how to find acceleration without time..or how to find Force..am i on the right track here?

any help please! thanks!

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

Join Physics Forums Today!

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

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

# Homework Help: Rotational kinetic energy and power

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