# Angular Acceleration problem.

1. Apr 21, 2013

### Aseri

A wheel is spinning at 44 with its axis vertical. After 15 , it's spinning at 60 with its axis horizontal. Find (a) the magnitude of its average angular acceleration and (b) the angle the average angular acceleration vector makes with the horizontal.

Just trying to work out what I'm doing wrong here to find the average angular acceleration.

I used angular acceleration = final velocity - initial velocity all divided by the time pasted.
(Also converted units from rpm to rad/s2 by multiplying by (2∏/60)

So far my initial answer is 0.11 rad/s2 which is apparently wrong, any idea what I can be doing wrong here?

2. Apr 21, 2013

### Simon Bridge

What are the units here?
44rmp, 15mins, 60rpm ...
something else?

Reading on - perhaps it is a mixture of unit types - rpm for frequency and s for time?
It is best practice to include units in the description.

Did you include the change in orientation too? Angular velocity is a vector.

If it were linear motion and I said I'd been going 44m/s north and 15 seconds later I was going 60m/s south ... would the average acceleration be (60-44)/15 ?