# Elastic Potential- Acceleration with springs

1. Nov 6, 2013

### hsphysics2

1. The problem statement, all variables and given/known data
A 1.6kg mass is suspended from a spring inside a stationary elevator. The spring stretches 12cm. The elevator now accelerates upwards, and the spring extends a further 12cm. What is the elevator's acceleration?

2. Relevant equations
Fy= may
Ue= 1/2 (kx2)

3. The attempt at a solution
I'm just not sure on the best way to start this question.

2. Nov 7, 2013

### AATroop

I would start with the first equation you provided. $F_y = ma_y$. What's the acceleration ($a_y$) in this problem? Where you can find a force on the system?

3. Nov 7, 2013

### hsphysics2

Fy=may
kx-mg=may
ay=(kx-mg)/m

but k is not given....

4. Nov 7, 2013

### AATroop

You need to find k first. What's the spring doing BEFORE the elevator starts moving?

5. Nov 7, 2013

### hsphysics2

Fy=may
kx-mg=0
k=(mg)/x
k=1306.666 N/m

Fy=may
kx-mg=may
ay=(kx-mg)/m
ay=9.79999 m/s2

6. Nov 7, 2013

### AATroop

I got a different value for k, could you double check it? My answer was a magnitude different.

7. Nov 7, 2013

### hsphysics2

oops, so k=130.666 N/m

8. Nov 7, 2013

### AATroop

Right, and you also know the distance so now would be a good time to find the potential.

9. Nov 7, 2013

### Staff: Mentor

Looks to me like you're done. No need for the potential in this problem.

10. Nov 7, 2013

### AATroop

Ah, yep. I was hasty.