# Elastic potential question

1. Nov 12, 2005

### F.B

I'm stuck on this question. I think it may be a bit easy but i still can't figure what im supposed to do.
Heres the question.

A horizontal sprinh, of force constant 12 N/m, is mounted at the edge of a lab bench to shoot marbles at the targets on the floor 93.0 cm below. A marble of mass 0.0083 kg is shot from the spring, which is initially compressed a distance of 4.0 cm. How far does the marble travel horizontal before hitting the floor?

2. Nov 12, 2005

### daniel_i_l

show some work!
Hint:
You know that the potential energy of the compressed spring is equal to the the kinetic energy of the marble after it is released. use that to find the initial speed of the marble. Then use kinimatics to find the distance.

3. Nov 13, 2005

### F.B

Before doesn't Et1= Ek1 + Ee and then Et2 = Ek2 + Eg. Am i missing something here

4. Nov 13, 2005

### dx

How much work do you have to do to compress this spring a distance of 4 cm? That is precicely the energy that is stored in the spring as potential energy. When the spring is released, it gives away the stored energy to the ball. Now what velocity would the ball have attained when it leaves the spring? After you figure out this velocity, you have to figure out the time for which the ball is in the air. In this time, the ball would travel a horizontal distance that depends on the horizontal velocity it has (which you figured out by considering the energy that it got from the spring).