# Circular motion of a tire

1. Nov 20, 2005

### hshphyss

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 20, 2005

### lightgrav

1) is not quite right ... 5.5 (2 pi) [rad] /1.2 is the average angular speed,
not the final angular speed. (why convert [1/s] to [1/min] to [1/s] ?)

2) if you convert 16 pi [rad/s] into 8 [rev/s], you might realize how far it travels in 5 seconds. Don't forget that the average speed was 4 [rev/s]