# Conservation of energy and conservation of momentum

#### sauri

Using both cinservation of energy and conservation of momentum, show that the spring constant k is given by k=2mg/H[1+mg/(m+M)H]

I thought that this would go easier if I rewrote the expression for kinetic energy in terms of momentum, but I cant exactly get around figuring the change in momentum to build an equation. would (m1v1/2) be correct?

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#### Hootenanny

Staff Emeritus
Gold Member
Do you have defintions for your symbols?

#### sauri

as in initial mass and initial velocity?

#### topsquark

sauri said:
as in initial mass and initial velocity?
"Initial mass?" :surprised: Perhaps you'd better tell us what the question is.

-Dan

#### Hootenanny

Staff Emeritus
Gold Member
topsquark said:
"Initial mass?" :surprised: Perhaps you'd better tell us what the question is.

-Dan
Hmm, a mass spring system oscillating at close to the speed of light. I've never done relativistic effects with SHM before...could be interesting...:surprised

#### sauri

It seems I have taken a wrong approach. I need to show that the spring constant k can be given by 2mg/H[1+mg/(m+M)H] using thr conservation of energy and momentum.

#### Hootenanny

Staff Emeritus
Gold Member
Does the question not give you any definitions for the symbols used?

#### sauri

I worked it out. No matter

#### topsquark

sauri said:
I worked it out. No matter
Then at least have the decency to tell us! You've got ME curious, anyway.

-Dan

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