# General Physics problem

1. Dec 12, 2006

### sixstringartist

Im having difficulty with a physics problem and was looking for help.

The problem states: A spring has a relaxed length of 1.0m, when no force is acting to stretch or compress it. It has a spring constant k = 200N/m. A ball of mass .05kg is attached to one end and it is made to go in circle with radius 1.4m, the new length of the spring. Assume that gravity and air resistance can be igmored. What is the magnitude of the force exerted by the spring on the ball?

This I got: F_mag = k_s * delta s = 80N

The follow up problem is: For the ball in circular motion in the problem above, what is its speed.

This is what gets me. I dont know how to find velocity without knowing the period.

Any help is greatly appreciated.

2. Dec 12, 2006

### Staff: Mentor

Hint: The motion is circular. What's the acceleration of the mass?

3. Dec 12, 2006

### marlon

The centripetal force is equal to $$\frac{mv^2}{r}$$.
v:velcity

Can you take it from there ?
marlon

4. Dec 12, 2006

### sixstringartist

yes thats it! thank you! It all makes sense, b/c all I could find is v^2 = G *(M/R) for orbiting bodies which is basically the same formula. Thanks again.