A circus acrobat of mass M leaps straight up with an initial velocity of vo from a trampoline. As he rises, he takes a trained monkey of mass m off a perch of height h above the trampoline. What is the maximum height attained by the pair in terms of M, m, Vo, h, and g?
The Attempt at a Solution
I used energy conservation upto the point where the acrobat reaches the perch and found out his imediate velocity at the perch to be v=square root(Vo^2 - 2gh) . The problem lies after this.
I looked up the solution to this problem and at this point conservation of linear momentum has been used as follows
Mv0 = (M + m)v' , where v' is the common velocity of the acrobat and the monkey immediately after the acrobat has taken the monkey off the perch.
The question I want to ask is, how can the momentum be conserved, when there IS a net external force on the syetm of (acrobat + monkey)? The net external force is (M + m)g downwards, so can we apply the conservation of linear momentum?