Springs >_<

[Stick]

I still don't get them... Can someone help me out with this question? Thanks.


A 5.0kg trolley approaches a spring that is fixed to a wall. During the collision, the spring undergoes a compression, , and the trolley is momentarily brought to rest, before bouncing back at 10m/s. The spring obeys Hooke's Law, and exerts a force of 10.0kN when the spring is compressed 5.0cm. Ignore friction and air resistance, and take gravity as 9.8m/s^2.

1. Calculate the elastic potential energy stored in the spring when its compression is equal to 2.0cm.
2. What is the elastic potential energy stored in the spring when the trolley momentarily comes to rest?
3. At what compression will the trolley come to rest?
4. The spring actually snaps upon compression. Explain why.

[pi]

This doesn't help, but this was my approach to these questions in year 11:

[Lasercookie]

1) Spring constant:

Energy:

2) It'll have to store enough energy to get the trolley bounce back at 10 m/s (spring potential --> kinetic energy, we'll get the answer by working it out backwards)


3) It had this much energy when it was at rest
edit: fixed mistake, made an error using the calculator

4) Hmm. I'm not too sure on what the best answer here would be. We know it's not an ideal spring if it snapped. Maybe something along the lines of Hooke's law only applies for small values of , beyond that the relationship between Force and Compression usually isn't linear. So perhaps an extension of 5cm went beyond that limit there, which is why what we predicted using Hooke's law didn't work.

[Stick]

Thanks for your answers, laseredd. However, I'm not too sure about your answer for question 4. The solutions are very vague, but it has to do with the wall and the way the trolley actually hits the spring. Would you be able to explain that in a Physics-like way?