A plank of length 2L leans against a frictionless wall at a height h.
It starts to slip downward without any friction. This will happen for some time, but suddenly the plank will lose contact with the wall, and fall to the ground all of a sudden! You can try to observe this at home too.
The problem is to calculate the height at which the plank loses contact with the wall.

Question

A plank of length 2L leans against a frictionless wall at a height h.
It starts to slip downward without any friction. This will happen for some time, but suddenly the plank will lose contact with the wall, and fall to the ground all of a sudden! You can try to observe this at home too. 
The problem is to calculate the height at which the plank loses contact with the wall.

mani_jha · Answer

|dw:1332297485832:dw|
I think this is a really tough problem. The book from which I have taken says that 'it is a tricky question which needs you to use all the concepts you've learned in rotational mechanics so far'
However, this sum is very good for practicing rotational mechanics. Think on this, it's not a problem if you can't do this, but if you don't even try, it is!
Hint: Try to analyze the motion of the center of mass.

aravindg · Answer

good question mani

aravindg · Answer

actually i hav dpne a very similiar problem

aravindg · Answer

which book u got this qn?

mani_jha · Answer

An Introduction to Mechanics by Daniel Kleppner

anonymous · Answer

@JamesJ @nikvist @Jemurray3

anonymous · Answer

I will be back

mani_jha · Answer

They ain't members of this group. Will they come?

aravindg · Answer

james has been away for sometime

anonymous · Answer

No harm in trying ;-)

aravindg · Answer

agreed

anonymous · Answer

|dw:1332332991816:dw|Forces acting on the Plank must be $N_{ground}, N_{wall}$ and $W_{gravity}$ or $W_{g}$.