# Homework Help: Rotational kinematics and grinding wheel

1. Jan 31, 2004

### ACLerok

i've been doing some physics problems out of the text and I was wondering: If an electric fan were to be turned off and you knew its angular acceleration, it is possible to find the number of revolutions it makes in a certain time interval?

also, i having a difficult time with this problem.

At t=0 a grinding wheel has an angular velocity of 22. rad/s. It has a constant angular acceleration of 32. rad/s^2 until a circuit breaker trips at time t=1.7 s. From then on, it turns through an angle 433. rad as it coasts to a stop at constant angular acceleration.
I was able to find the total angle the wheel had turned between t=0 to the time it comes to a rest to be 516.64 rad, but now i have to find at what exact time it comes to a stop.. any pointers and tips are greatly appreciated.

thanks

2. Jan 31, 2004

### ShawnD

1. find the rotation speed when the breaker tripped (Wf = Wi + a*t)
2. find the deceleration from when breaker tripped (Wf^2 = Wi^2 + 2ad)
3. find the time it took took to decelerate (d = Wi*t + (1/2)a*t^2)

That should work.