# Homework Help: Mass launched up a ramp by a spring(friction)

1. Nov 1, 2007

### BBQX

1. The problem statement, all variables and given/known data
A block M=2kg rests against a spring (K=2000n/m) compressed by 10cm. When released, the block is propelled up a rough(Mu-k=0.1) incline. What is the max height reached by the block?
https://www.physicsforums.com/attachment.php?attachmentid=11412&stc=1&d=1193953938
2. Relevant equations
Well I was trying to solve this using Conservation of energy.
Ei+W=Ef

friction = muN
N= mgcos(th)
L= length of ramp
H= height

3. The attempt at a solution

.5(2000)(0.1)^2= 2(9.8)Hsin(10)-(Fiction)Lcos(180)

I'm stuck here
and really confused... am i missing a term and how do i find "L"

2. Nov 4, 2007

### dynamicsolo

I take it that you set the initial potential energy stored in the spring equal to the initial kinetic energy of the block when it departs from the spring. You then noted that both the work against gravity and the work done by friction will ultimately reduce the kinetic energy of the block to zero, thus determining where it will stop. So the work terms must equal the initial kinetic energy of the block on starting up the incline.

First question: was an angle for the incline given? It will make a difference because the kinetic frictional work does depend on the path taken by the block.

Second, don't forget that some of the spring's potential energy went into lifting the block against gravity while it was still in contact with the spring. Or is the spring on a horizontal surface and then the block starts up the incline after the spring is relaxed?

Third, I'm not clear from the way the problem is written whether they want the change in height of the block or the distance along the incline that the block slides.

By the way, your attachment doesn't display.