# An question

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2. ### dextercioby

12,317
The first question is not difficult,however a correct answer to it would solve point b).Without it,u couldn't be able to solve point b).

What are your ideas to approach the problem?You don't expect us to solve it for you,though it's 'urgent'.

Daniel.

PS.Do you know Steiner's theorem??It can be useful for point b).

3. ### mfk_1868

21
anyone can solve 5th question

4. ### dextercioby

12,317
Obviously i can solve the problem for you,however i won't do it.I'll just guide through it.The question at the point "b".Taking into account that is an elastic collision,what phyisical quantities are conserved...?

Daniel.

PS.I hope u see my point.I won't be in your shoes tomorrow at the exam.

5. ### mfk_1868

21
can you tell me the answer i found it right now 12M/13 can you check this?

6. ### dextercioby

12,317
How did u get that answer??I'm not saying it's good,i'm not saying it's bad,just wanna know how u got it.The method is far more important than the result itself.

Daniel.

7. ### mfk_1868

21
i cant post it but i made 3 equalities angular momentum cons lineer momentum cons and K.E cons now can you tell the answer please it is very importqnt

8. ### mfk_1868

21
con=conservation

9. ### dextercioby

12,317
Why didn't u say that in the first place??You made me think that u were totally 'lost'... :tongue2:
From the angular momentum conservation,u got the angular velocity of the ruler,okay??
From the conservation of linear momentum u got the linear velocity of the ruler,okay??
With these 2 values,u got back into the KE conservation law and using the Inertia moment with a correct value,u got "m".In that case i get
$$m=\frac{M}{1+\frac{12d^{2}}{L^{2}}}$$

Daniel.

PS.One of us is wrong...Don't know who. I may have messed up my calculations,though.

10. ### dextercioby

12,317
I found rather dubious that your answer does not depend upon the distance parameter 'd'.If 'd=0 (the puck hits the stick in its center of mass),then the stick should not rotate and the masses should be equal.
My answer satisfies this logics.Yours not.

Daniel.