# A spring in an elevator

1. Apr 11, 2013

### nubshat

A 1.6kg mass is suspended from a string in a stationary elevator. The spring stretches 12cm. The elevator now accelerates upward, and the spring extends a further 12cm. What is the acceleration in the elevator?

2. Apr 11, 2013

### tia89

You should show you tried at least to solve the problem if you want an answer... if we know where you have the problem, we can help you understand it

3. Apr 11, 2013

### nubshat

Ignore this post

4. Apr 11, 2013

### nubshat

I tried to solve it, but I'm not succeeding. So far I have managed to calculate the force constant of the spring, but I don't know what to do next

5. Apr 11, 2013

### tia89

Ok then, if you now have the force constant of the spring you can pass to the accelerated elevator case... what happens when you observe an accelerated frame? Remember the equivalence principle, stating that an acceleration in one direction is equivalent to an additional gravitational field in the opposite direction... which "apparent" gravitational field do you need to elongate the spring further? How do you balance all the forces to be stationary again?

6. Apr 11, 2013

### ap123

Draw a free-body diagram for the mass and then use Newton 2.