# Homework Help: Block ramp friction and spring

1. Oct 20, 2009

### bricker9236

1. The problem statement, all variables and given/known data
A 5 kg block is placed near the top of a frictionless ramp, which makes an angle of 30o degrees to the horizontal. A distance d = 1.3 m away from the block is an unstretched spring with k = 3000 N/m. The block slides down the ramp and compresses the spring. Find the magnitude of the maximum compression of the spring.

2. Relevant equations
h=d+xsintheta
PE=mgh=mg(d+x)sintheta
PE=1/2kx

mg(d+x)sintheta=1/2kx
0=1/2kx+-mg sintheta +-mgd sintheta
ax+bx-c

3. The attempt at a solution

What i did was plug in the numbers into the quadratic equation and i thought that is all that i had to do.. and the answer is still not correct. if someone could please help me out that would be appreciative =)

2. Oct 20, 2009

### ehild

Your formula for PE is wrong. PE=1/2kx2.

ehild

3. Oct 21, 2009

### bricker9236

I just tried figuring it out once again..

a=1500
b=48.463
c= 63.002

so then i used the quad equation to solve for X

x= -b +- squareroot b2-4ac / 2a

and x comes out to either be

x= .0506461
x= -.0829547

then i put it back into the equation
PE=.5(k)(x)

and i tried both.. one i got around 3 and the other i got around 10

what else am i doing wrong that i cant figure this out?

4. Oct 21, 2009

### ehild

What does it mean "maximum compression of the spring"? And what is "x" for?

ehild