Finding kinetic energy retained by an object after an elastic head-on collision

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SUMMARY

The discussion focuses on calculating the percentage of kinetic energy retained by a 0.10 kg object after an elastic head-on collision with a 0.15 kg object. The initial velocity of the first object is 0.20 m/s, and after the collision, its final velocity is -0.0025 m/s, while the second object's final velocity is 0.198 m/s. To find the retained kinetic energy, one must apply the conservation of energy and conservation of linear momentum principles, calculating the final kinetic energies using the formula (1/2 * mv^2) and comparing them to the initial kinetic energy of the system.

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JuniorJumper
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Hi, I am new to the forums & I have a question about the following problem:

A 0.10 kg object moving initially with a velocity of 0.20 m/s makes an elastic head-on collision with a 0.15 kg object initially at rest. What percentage of the original kinetic energy is retained by the 0.10 kg object?

m1=0.10 kg
vi1=0.20 m/s
v1f=-0.0025 m/s

m2=0.15 kg
vi2=0.00 m/s
v2f=0.198 m/s

I calculated the final velocities of both objects after the collision, but can not decide how to find the kinetic energy retained by m1. I tried finding the kinetic energy lost by m1 (0.002) but then I didnt know where to go from there. I know this must be a simple problem, but I am just not seeing it? Thanks for any guidance :)
 
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You must use conservation of energy AND conservation of linear momemtum. Once you have calculated the final velocities correctly (your's appear to be incorrect :cry:) then you can calculate their respective kinetic energies (1/2*mv^2). You can then compare each final kinetic energy to the initial system energy (K1/Kinitial and K2/Kinitial) to obtain your percentages (note that they should add to 100%). Also, since energy is conserved the sum of the final kinetic energies will equal the initial kinetic energy (of the incoming object). Hope this helps! Good luck!
 

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