# Homework Help: Is this tangential velocity or angular velocity?

1. Nov 14, 2005

### donjt81

Here is the homework question...

According to the Guinness Book of World Records, the highest rotary speed ever attained was 2010m/s(4500mph). The rotating rod was 15cm(6in.) long. Assume the speed quoted is that of the end of the rod. What is the centripetal acceleration of the end of the rod?

So I think since they say rotary speed they are talking about angular velocity here. so i would say angular velocity (w) = 2010m/s. Is this correct? or is it tangential velocity (v) = 2010m/s?

is there a certain way to tell the difference between tangential velocity and angular velocity in a question.

2. Nov 14, 2005

### Chi Meson

Yes, look at the unit. Here it is 2010 m/s. This is a linear velocity unit. angular velocity is in angular units per unit of time, such as "rotations per second", "revolutions per minute", "degrees per second." The SI unit for $$\omega$$ is radians per second.

3. Nov 14, 2005

### donjt81

Thank you that makes it easier to tell.

Also I was looking at it again and another question popped in my head.

When i first looked at the problem I was assuming that radius=15cm but then after looking at it some more i was thinking is it diameter = 15cm or is it radius = 15cm

does anyone know?

4. Nov 14, 2005

### Chi Meson

There is no way that the diameter is 15 cm. Either the rod is rotating about its end and the radius is 15 cm, or the rod is roatating about its middle, and the radius will be 7.5 cm.

5. Nov 15, 2005

### donjt81

umm... thats the same thing. diameter is 15 means that radius is 15/2=7.5

6. Nov 15, 2005

### Chi Meson

Um, yes I was, um,... seing if...

I was checking to see if... you were...paying attention.

Very good.

[I have no idea what I was thinking last night! ..it happens]

7. Nov 18, 2005

no worries