# Homework Help: Spring Problem Help

1. Oct 31, 2012

### CAPA

1. The problem statement, all variables and given/known data

A massless spring of length 0.270 m is in its relaxed position (left diagram). It is compressed to 71.0 percent of its relaxed length, and a mass M = 0.140 kg is placed on top and released from rest (shown on the right). The mass then travels vertically, taking 1.20 s to reach the top of its trajectory. Calculate the spring constant
Diagram http://www.learning.physics.dal.ca/dalphysicslib/Graphics/Gtype13/prob24_CompSpring.gif

2. Relevant equations

3. The attempt at a solution

I tried using conservation of energy, but kept getting stuck not being able to find how high it goes or the velocity when it leaves the spring

2. Oct 31, 2012

### tiny-tim

Welcome to PF!

Hi CAPA! Welcome to PF!
It will leave the spring when the deceleration of the end of the spring is … ?

3. Oct 31, 2012

### CAPA

Re: Welcome to PF!

we haven't really done any decelerating questions with springs. How would I go about finding that? would it be equal to gravity?

4. Nov 1, 2012

### tiny-tim

Hi CAPA!

(just got up :zzz:)

Use Fnet = ma to find the acceleration at a general displacement x.

The mass will leave the spring when that acceleration becomes less than -g.