# Homework Help: Energy Problem with Spring, Gravity, and Friction

1. Dec 4, 2017

### FettuccineAlfredo

1. The problem statement, all variables and given/known data
An elevator is traveling at 30 m/s just as it touches a cushioning spring. The safety clamps engage at that moment and provide 20,000N of frictional force. The mass of the elevator is 3000kg and the spring constant is 15000 N/m. How fast will the elevator be traveling after the spring compresses 0.8m ?

2. Relevant equations
K1+Wf = Ug2+Us2+K2
Allow the point that the elevator touches the spring to be y=0
3. The attempt at a solution
1/2*m(v1)2+Ffd=mgy2+1/2*kx2+1/2*mv22
Manipulating this around and plugging in numbers gives an answer of 30.03 m/s for me. Am I missing something here?
Edit: d is just the distance along which friction occurs, -.8 m?
x is the compression of the spring, also .8m
y2 is the distance traveled by the elevator, so -.8m

Last edited: Dec 4, 2017
2. Dec 4, 2017

### Staff: Mentor

Hi FettuccineAlfredo,

Welcome to Physics Forums!

Can you define your variables used in the attempt at solution? For example, what distinguishes $d$, $x$, and $y_2$?

3. Dec 4, 2017

### Staff: Mentor

I didn't check your calculation, but realize that the work done by friction is negative. (As will be y2.)