# Finding a landing speed from spring constants

## Homework Statement

Problem: http://img147.imageshack.us/img147/8509/physjc9.gif [Broken]
Additional info: mass of the lander 7750 kg, 1.790967742 is the mag of acceleration due to gravity, this info was found in earlier parts of the problem

## Homework Equations

I used these 2 equations and set them equal
[1/2(kx^2)] * 3 = 1/2mv^2

## The Attempt at a Solution

[1/2(11566.7)1.2^2] * 3 = 1/2(7750)v^2
solve for v, v= 2.53919 m/s, which was wrong
is the equation wrong?

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## Answers and Replies

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Well, as the spring compresses, there is an aditional energy which must be compensated for.

And how might I find this additional energy and apply it to the problem at hand?

D H
Staff Emeritus
You have forgotten the weight of the vehicle. At the point of maximum compression, the springs have fully absorbed the vehicle's kinetic energy just prior to contact and are supporting the vehicle's weight.

How do I apply the weight to the equation?

D H
Staff Emeritus
The vehicle will bounce a bit and eventually come to a rest with the springs compressed to balance the force due to gravity. What is the final compression of the springs?

.4 m?
(7750*1.790967742)/ (3 * 11566.7 ) = .3999988473

D H
Staff Emeritus