Determining non-conserved work from a collision

[JoeyBob]

Homework Statement

see attached

Relevant Equations

W=change in kinetic energy

So I know from a previous part of the problem that the kinetic energy right before the collision is 94.556.

The non conserved work would also equal the change in kinetic energy + change in potential energy.

What I don't understand is how the potential or kinetic energy would change during the collision. The potential energy is already 0 and wouldn't the kinetic energy just be transferred (so the object would slow down because its heavier).

answer is suppose to be -47.32

 

[haruspex]

wouldnt the kinetic energy just be transferred

Never assume work is conserved without good reason. In a coalescence, as here, you can use conservation of momentum to find the new speed, and you will see that KE has been lost.

 

[JoeyBob]

Never assume work is conserved without good reason. In a coalescence, as here, you can use conservation of momentum to find the new speed, and you will see that KE has been lost.

So from conservation of momentum I find that the final velocity was 3.075, which gives a final kinetic energy, which allows me to calculate the change, which let's me find the work.

 

[haruspex]

So from conservation of momentum I find that the final velocity was 3.075, which gives a final kinetic energy, which allows me to calculate the change, which let's me find the work.

Yes, but it is much better, for several reasons, to solve a problem purely algebraically, only plugging in numbers at the very end. Had you done that, you would have found it was unnecessary to find the velocities, neither before impact nor after.