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**1. The problem statement, all variables and given/known data**

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.

http://oak.cats.ohiou.edu/~tt106402/work/phys252/Physics%20Notes/ch10.pdf [Broken]

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.

http://www.cramster.com/answers-nov-09/physics/angular-momentum-uniform-rod-length-l1-mass-08-kg-attached_705957.aspx

**2. Relevant equations**

**3. 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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