Calculate Spring Constant: Massless Spring & 0.140kg Mass

[CAPA]

Homework Statement

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

Homework Equations

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

 

[tiny-tim]

Welcome to PF!

Hi CAPA! Welcome to PF!

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

It will leave the spring when the deceleration of the end of the spring is … ?

 

[CAPA]

Hi CAPA! Welcome to PF!


It will leave the spring when the deceleration of the end of the spring is … ?

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

 

[tiny-tim]

Hi CAPA!

(just got up :zzz:)

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

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