(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

A grinding wheel is a uniform cylinder with a radius of 8.70 cm and a mass of 0.400 kg.

a)calculate the moment of inertia about the center.

b)Calculate the applied torque needed to accelerate it from rest to 1950 rpm in 6.00 s if it is known to slow down from 1250 rpm to rest in 57.5 s.

3. The attempt at a solution

first i changed the given radius to .087 m..

a) wasnt that hard, I=mR^2, (.4)(.087)^2=.00151

b) since i was given the ωi=0, and ωf=1950 rpm→32.5 rps, and t=6s, i used the formula ωf=ωi+αt, and got α=5.42. i used my α to solve for a with the equation a=Rα (because F=ma) and got .47, then using F=ma, F=(.4)(.47)=.19. Since τ=RF, τ=(.19)(.087)=.02, which is incorrect.

Im guessing that my calculated I has something to do with the answer because of the way my professor asks the question, in parts where you use your answer in part a to solve for part b which is needed to solve for part c, etc, but i dont understand how my answer is wrong. however realistically i can understand how a τ of .02 wouldnt cause a cylinder to rotate from 0 to 1950 rpm in 6 sec.

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

Dismiss Notice

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: Angular velocity, acceleration. and moment of inertia

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