# Homework Help: Rotational Motion of a toy airplane

1. Apr 20, 2013

### SChiO

1. The problem statement, all variables and given/known data

We were given a video....I'm not sure if you can post video links otherwise I would...but it's a video of an airplane on a string flying in a circular motion. On the top of the string you can see that the tension of the string is 6.5N. and it is flying at an angle of 50°. We are told to find the angular velocity, mass of plane and length of string.

3. The attempt at a solution

Using ω=2pi(period) I found it to be 5.28 m/s with a period of 1.19s/rev
Using Newton's 2nd law and knowing that the force of gravity is equal to the y-component of the tension force I found the mass to be equal to .42 kg.
However I am stuck on finding the length of the string.......I have an idea that I need to find the radius of the circle and then from there I know I can find the length of the string but I'm not sure how to find the radius. I'm thinking to use this equation: v=rω but I'm not sure how to find the linear velocity or if that's even right.......HELP PLEASE!! I'll see if I can post the video for ease...Thanks

2. Apr 20, 2013

### Simon Bridge

You can post links to a video - but it is best to give a written description anyway.
Is that 50deg angle to the horizontal or the vertical?
Just a note - the units of $\omega$ is radiens per second. Since you were "given the angular velocity" I'm guessing you mean that the tangential velocity was 5.28m/s.
"Period" is usually just given in seconds.

Hint: centripetal force and acceleration.