# Homework Help: Model Airplane-Work-Energy Theorem and Kinetic Energy

1. Sep 27, 2008

### pstfleur

1. A model airplane is flying at a speed of 22 m/s on a horizontal circle of radius 16m. The mass of the plane is 0.90 kg. The person holding the guidelines pulls it in until the radius of the circle becomes 14m. The plane speeds up, and the tension in the guideline becomes four times greater. What is the net work done on the plane

2. KE=1/2(mv^2),
W=KE final-KE initial

3. Obviously the radius and tension is throwing me off in the problem. I know how to find the KE.. I know the answer is suppose to be 5.4*10^2J.. Can someone lead me in the right direction or help with this problem

2. Sep 27, 2008

### Mattowander

You can find both the initial kinetic energy and Centripetal force from what's given.

Then, you know the Centripetal (tension) force will become four times as great. That should help you calculate the new velocity, and therefore you can calculate the new kinetic energy.

The answer I got was 5.5 * 10^2 J but I might have just had rounding issues. Hope that helps!

3. Sep 27, 2008

### pstfleur

Thanks Alot..I got the right answer now..