Finding Spring Constant Without Distance

[mailmas]

Homework Statement

Spring Compressed = 20cm = .2m
Decompresses and leaves the ground at a velocity of 5m/s
Mass = 6.00 kg

Homework Equations

k = fx

The Attempt at a Solution

I have no idea where to go from here...

 

[Simon Bridge]

Hint: conservation of energy.

 

[mailmas]

Hint: conservation of energy.

Awesome will Google this and come back with an attempt!

 

[Simon Bridge]

Don't you know what the law of conservation of energy says?
Just work out where the energy in the spring goes.

 

[mailmas]

Don't you know what the law of conservation of energy says?
Just work out where the energy in the spring goes.

Energy is conserved and transformed into different types of energy within a conservative system?

Could I say the Ui = Kf? But how would I solve for the spring constant?

 

[Soumyadip]

Equate it's kinetic energy to its spring potential energy

 

[Simon Bridge]

Equate it's kinetic energy to its spring potential energy

... what about gravitational PE?

 

[Simon Bridge]

Energy is conserved and transformed into different types of energy within a conservative system?

... No. Total energy is always conserved in a closed system.

[math]Could I say the Ui = Kf? But how would I solve for the spring constant?[/QUOTE]
Technically you need the net loss in PE is equal to net gain in KE... you need summation signs in front of the variables.

What you have to do is think about what the energy changes are.
You know KE changes ... you have an equation for that. It starts out at rest, so KE=0, and ends op with speed v, so $$\Delta K = K_f - K_i = \frac{1}{2}mv^2$$ right? Sound familiar?

Since you are told there is a non zero speed at the end, there is a net gain in kinetic energy. This energy has to come from somewhere ... where does it come from?

What other energies change?

Note: there is a change in compression in the spring, and there is a change in height: what sort of energy changes do those imply?

I handy discipline is just to write down "before", then write E_b = then list all the potential energies and kinetic energies there are.
Leave a space.
Write "after" and put E_a = then list all the potential and kinetic energies.
Then write E_b = E_a
... and solve the equation for the variable you need.

 

[haruspex]

Decompresses and leaves the ground at a velocity of 5m/s
Mass = 6.00 kg

Use the enormous help you have already had to solve the problem, but I am curious about one thing. Is there any more detail to the original question? What is the exact wording?

 

[Simon Bridge]

Use the enormous help you have already had to solve the problem, but I am curious about one thing. Is there any more detail to the original question? What is the exact wording?

... yeah: I think that is as far as I can go without actually doing the problem myself.