Sliding on a sliding hemisphere

1. Aug 30, 2009

Nanyang

1. The problem statement, all variables and given/known data
A small mass m slides on a hemisphere of mass M and radius R is also free to slide horizontally on a frictionless table. An imaginary vertical line is drawn from the center of the hemisphere to its highest point, where the small mass is originally placed at rest. The angle A is the acute angle made by another imaginary line drawn from the small mass after it starts to slide down to the center of the hemisphere with the imaginary vertical line mentioned before. In other words, A= 0 originally. Given that cosA = k. Find the ratio of M/m.

2. Relevant equations
I'm not really sure.

3. The attempt at a solution
Here's what I did.

I imagine that the big mass moves at velocity V and the small mass with a tangential speed v after some time. Then using the conservation of energy I obtain,

mgR = $$\frac{1}{2}$$(M+m)V2 + $$\frac{1}{2}$$mv2

EDIT: I just spot my mistake on the mgR thing.

Next I obtain the condition when the small mass just begins to leave the hemisphere's surface,

gcosA= v²/R

I think my mistake is the above.

I then obtain another equation using the conservation of momentum in the left-right direction,

mvcosA=(M+m)V

Then I substituted and rearranged all the stuff and got:

$$\frac{(k-1)}{k(2-k)}$$2 = M/m

But it doesn't look correct.

EDIT: I think I found the mistake in the conservation of energy part. But still do give hints on how to solve it.

Last edited: Aug 30, 2009
2. Aug 30, 2009

Nanyang

I just solved it. Anyway, typing the problem down again here sure does help in solving it by making you think hard again. :rofl: