# Finding revolution time at surface

## Homework Statement

For a 0.90km radius cylinder, find the time for one revolution if "gravity" at the surface is to be 9.8 m/s2.

rω^2=a

## The Attempt at a Solution

i tried solving for omega but i couldnt find a solution that i only had 1 variable in it.

haruspex
Homework Helper
Gold Member
2020 Award

## Homework Statement

For a 0.90km radius cylinder, find the time for one revolution if "gravity" at the surface is to be 9.8 m/s2.

rω^2=a

## The Attempt at a Solution

i tried solving for omega but i couldnt find a solution that i only had 1 variable in it.
Which other variable do you think you have no value for?

Which other variable do you think you have no value for?
i dont know the velocity for solving for omega, is this what you meant?

gneill
Mentor
ω is a velocity: an angular velocity. How is ω related to the frequency and the period of one "cycle" (one revolution in this case)?

haruspex
Homework Helper
Gold Member
2020 Award
i dont know the velocity for solving for omega, is this what you meant?
I don't know where you are stuck. The first step is to calculate ω - can you do that from the formula you quoted? Next, as gneill says, you can find the time of one revolution from ω. Is that part your problem?

i know that ω = v/r but i do not know v. I guess i am confused about what to do in order to solve for ω.

haruspex
Homework Helper
Gold Member
2020 Award
i know that ω = v/r but i do not know v. I guess i am confused about what to do in order to solve for ω.
In the OP you quoted the right equation to be using. That has three variables and you are given the values of two of them. Forget v for now.

wow can't believe i missed that. so then 450ω^2=9.8, ω=.133
i converted .9 km to 900 m

Last edited:
haruspex
Homework Helper
Gold Member
2020 Award
wow can't believe i missed that. so then 450ω^2=9.8, ω=.133
i converted .9 km to 900 m
Ok, but why did you halve it to 450? Either way, I don't get .133.

Ok, but why did you halve it to 450? Either way, I don't get .133.
the cylinder's diameter is 900m and i need the radius. 900/2=450. then i did 9.8/450=ω^2=.022, ω=.147
(i had a math error in the previous post, this is what i actually got)

haruspex
Homework Helper
Gold Member
2020 Award
the cylinder's diameter is 900m

then i get .104

haruspex
Homework Helper
Gold Member
2020 Award

then i get .104
Sounds right.

so after this do i just plug it into the equation? the answer i get seems high

haruspex