# Homework Help: Circular Motion Help

1. Nov 19, 2005

### hshphyss

Circular Motion Help!!

Can anyone help me with these problems?

1.A tire placed on a balancing machine in a service station starts from rest and turns through 5.5 revs in 1.2 s before reaching its final angular speed. Assuming that the angular acceleration of the wheel is constant, calculate the wheel's angular acceleration.

--- I know you have to chance rev per s into revs per min into rad per s. So i did 5.5/(1.2/60)=275 rpm x (2pi/60)=28.8 rad/s. Is that right?
After I got that i used the formula vf=vi+at so 28.8=0+1.2. My time might be wrong but I was sure what to do.

2. The tub within a washer goes into its spin cycle, starting from rest and reaching an angular speed of 16pi rad/s in 5.0 s. At this point, the lid is opened, and a safety switch turns off the washer. The tub slows to rest in 14.0 s. Through how many revolutions does the tub turn? Assume constant angular acceleration while the machine is starting and stopping.

I chanced 16pi into 50.3 rad/s, and converted that to 480 rpms. The next part is where I get stuck. How would I set up the constant angular acceleration problem to help me get the revelutions. I know how to find the acceleration, but what would I do next?

3. (a)Find the centripetal accelerations of a point on the equator of Earth.
(b) Find the centripetal accelerations of a point at the North Pole of Earth.

2. Nov 19, 2005

### kp

1) i no expert but, i think your using the wrong equation for this problem, your given a distance (5.5 revolutions in 1.2s) I would think that an equation that uses distance & time to find acceleration would be better, also you might check your conversions to rads again.

2) your given final angular speed and time, use a equation to find acceleration, then find distance distance (or revolutions). then convert to rpms.