sos..ball falling from the sky

[unDRdog]

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ok...so a ball falls from the sky onto a spring (say on a table) and compress the spring "down" untill it stops. right before recoil the spring has moved distant "x"..Heres my ?...how is energy conserved..wouldnt this be an inelastic collesion therfore not conserving energy?...AHHHH WTF..simple ? anybody have a good way of thinking of elastic/inelastic?sos

 

[loveoforganic]

If you assume the spring is perfect and upon compressing doesn't lose any of the ball's energy to heat, can you see how energy would be conserved?

100% gravitational potential energy at it's top point in the sky => 100% kinetic energy right before it hits the spring => 100% spring potential energy when it reaches 0 velocity after compressing the spring

 

[sv3]

the above poster was perfect in their explanation

also, you seem to be confusing this for momentum type problems where two objects stick together after a collision. Don't look at springs like that. There is no permanent stickage (prolly not a real world) here.

 

[unDRdog]

thanks-- i think i am getting this confused with conservation of momentum... so basically energy is conserved in a system as long as it doesnt loose heat? (as far as springs go) i know overly simplistic but am i on the right track?

 

[loveoforganic]

Well, heat is the biggest one to look for. Two other common ways energy could be lost from a system are in the form of sound or electromagnetic radiation.

 

[sv3]

i think the question would generally "lead" you to include something that would modify a simple problem. For example, if your given the coeffecient of friction, you should consider that force - doesn't mean its always there but you generally need that information for a calculation. For a qualititative question loveoforganic's repsonse was good.

 

[Bildo]

You might want to consider that with a perfect string, the 'collision' happens over a long period of time (so a different impulse). The spring compresses during the collision then pushes it away.

At the extremes...you could thing of a nonspringy floor that bounces away a ball as having an extremely high spring constant k, so the collision is almost instantaneous, whereas a 'springy' ground with a smaller k would compress farther.

Pretty sure, anyways.