Finding frequency if you know mass and length of rope.

[astru025]

Homework Statement

A girl with a mass of 40 kg is swinging from a rope with a length of 2.8 m. What is the frequency of her swinging?

Homework Equations

I could find the period of the situation and then from there could calculate the frequency. For the period I'm not sure what equation I should use. I tried using the equation T=2∏ (√I / mgh ). This did not work for me though. Any help would be nice!

The Attempt at a Solution

Attempt shown above.

 

[Doc Al]

I tried using the equation T=2∏ (√I / mgh ). This did not work for me though.

That's the formula for a physical pendulum, which should work just fine. Show what you did.

Of course, since you are ignoring the mass of the rope (I presume), you can also treat this as a simple pendulum.

 

[astru025]

Okay I used the equation for a simple pendulum: T= 2 x pie x square root of L / g. Square root of 2.8 / 9.8 x 2pie gave me 3.35 for a period. Then I plugged in 1/3.35 for the frequency and came up with the right answer. Thanks so much!