# Elastic potential energy

## Homework Statement

A horizontal spring, of force constant 12N/m, is mounted at the edge of a lab bench to shoot marbles at targets on the floor 93.0 cm below. A marble of mass 8.3 x 10^-3kg is shot from the spring, which is initially compressed a distance of 4.0 cm. how far does the marble travel horizontally before hitting the floor?

Ee= 1/2kx^2
Ep=mgh
Ek=1/2mv^2 ?
W= Fd?

## The Attempt at a Solution

not sure how to start it off

First let us find the initial velocity with which the marble is projected.

What principle do you think we will use?

Doc Al
Mentor
Start by figuring how fast the marble is moving when it leaves the spring.

ok i did that and i got 1.52m/s by using the law of conservation energy "Ee=Ek"

correct

Doc Al
Mentor
ok i did that and i got 1.52m/s by using the law of conservation energy "Ee=Ek"
Good.

Now you can treat the rest as a projectile motion problem. How long does it take for the marble to hit the floor?

Now this is the speed with which the marble is projected horizontally onto the floor below.

we never have touch upon projectile motion in class. is there some other method?

in projectile motion the vertical motion is independent of the horizontal motion.

Hence one can treat projectile motion as the resultant of two linear motions. So just work in linear motion. But be careful whether you are working in the vertical or in the horizontal.