Motion's frequency

1. Sep 25, 2013

vanitymdl

A electric model train travels at 31.7 cm/s around a circular track of radius 1.73 m.

How many revolutions does it perform per second, i.e, what is the motion\'s frequency?
______ Rev / s

Find the train\'s period of revolution.
______ s

This is how I worked out the problem:
v^2/r = rw^2
.317^2/1.73 = 1.73w^2
.317^2/1.73^2 = w^2
w = 0.18323699421 radians per second.

34.3 seconds
1.75 revolutions per second (60/34.3)

I'm getting that 1.75 rev/s is wrong and I don't know why or how

2. Sep 25, 2013

Dick

I would just use v=rw. It's a more basic formula. But it's going to give the same thing. You've got 34.3 seconds for the period ok. And 60/34.3 would be ok if you wanted revolution/minute because there are 60 seconds in a minute. But that's not what they are asking for. Can you fix it?

3. Sep 25, 2013

vanitymdl

But I thought 60/34.3 would give me the seconds? So what you're saying is that I have to convert 60/34.3 re/min to rev/sec? Isn't that what 34.3 is, it's seconds

4. Sep 25, 2013

Dick

If a revolution takes 2 seconds, how many revolutions per second? There is really no 60 needed.

5. Sep 25, 2013

vanitymdl

Okay so if it take 2 seconds per revolution. I would take my seconds which is 34.3 and multiply it by 2?

6. Sep 25, 2013

Dick

Noo. If it takes 2 seconds to make a revolution, then in 1 second it will make 1/2 revolution. So that's 1/2 revolution per second. Not 60/2. Just think about it. This is a different question.

7. Sep 25, 2013

vanitymdl

Okay well I'm still getting it wrong but thank you anyway

8. Sep 25, 2013

Dick

You're welcome. But think about this. Where did the 60 in your problem even come from? I think you are just plugging into formulas without thinking about what they mean.

9. Sep 25, 2013

vanitymdl

What I understood is I get 34.3/2 and get 17.5 but that's still the wrong answer

10. Sep 25, 2013

Dick

The 2 was just a simple example to try to get you to understand where the formulas are coming from. Here, I'll spell it out: if p is period in seconds, then 60/p is revolutions per minute. 1/p is revolutions per second. Can you understand why?