Okay I just need someone to explain to me 2 things in the solution to a problem.
Here is a link to the solution manual for the book I am using for my University Physics 1 course.
if you search (crtl F) type in "A uniform rod of length L1 and mass", and it will take you to problem 55.
I must also note that the solution in the back of my book has L2/L1=0.36, and this solution manual online has it = 0.88, so I hope the one online is wrong, because as you will read below, I don't see the connections.
Heres a picture of the problem...its the only one I could find but you have to have cramster.
The Attempt at a Solution
I honestly don't understand part 1. It seems to indicate that the gravitational torque of the rod = the rotational kinetic energy right before impact. Why is this? I understand that when the bar is directly below the pivot, the torque=0, so is it at that exact point that ALL of the gravitational torque gets "converted" into rotational kinetic energy? I just haven't seen this in a problem before, and there is nowhere in my book that I have found a direct relationship between torque and kinetic energy. Clearly I must be missing something.
I understand part 2, that angular momentum right before and after impact is conserved(because torque=0).
I also don't understand part 3. It seems to have "plugged in" the angular velocity solved for in part 1 into part 2, and used that to = something.
If any advice can be given on this problem it would be GREATLY appreciated, as my final exam is tomorrow..
Lastly, I don't know why alpha=m/M is used.
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