# Motion's frequency

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.
there are 2 pi radians, so it takes 2pi radians / .1832 radians/second = seconds

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

## Answers and Replies

Dick
Homework Helper
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.
there are 2 pi radians, so it takes 2pi radians / .1832 radians/second = seconds

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

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?

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

Dick
Homework Helper
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

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

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

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

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.

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

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

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.

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

Dick