Spring launches 2kg object after compressing 5m, find launch velocity

[avb203796]

When a 80.0kg mass is placed (not dropped) on topof a spring, the spring is depressed by 20 cm. The same spring is then used to launch a 2.0 kg object vertically. If the spring is compressed 5.0 m by pushing it down, and the object is then placed on top and the spring released, what will be the launch velocity of the 2.0kg object? Draw and label the force diagram as part of your answer.

I do not really ge twhat I am supposed to do here and I have no clue where to start. Any help would be greatly appreciated!

 

[andrewchang]

try using energy to solve for the spring constant.

 

[avb203796]

But how would I find the energy?

 

[andrewchang]

$$mgh = \frac {1}{2} kx^2$$

 

[avb203796]

But what would be my h and what would be my x?

 

[avb203796]

I am not given the h or the x am I?

 

[daniel_i_l]

The x is the amount that the spring is compressed. In this case the h is the same as the x, because the only change in the masses height is because off the compression of the spring.

 

[avb203796]

Ok thanks!

 

[avb203796]

Wait, am I using the 8o.o kg and the 20cm or the 1.0kg and the 5.0m?

 

[daniel_i_l]

80.0kg and the 20cm

 

[avb203796]

so then I get 68.6 for k but then what do i do with that?

 

[kp]

Force = kx
F/x = k

what is the Force...check your units.

 

[avb203796]

I am not sure what you mean?

 

[andrewchang]

once you find the spring constant, you can use it for the second part of the problem.

 

[daniel_i_l]

Hint: Conservation of mechanical energy.