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# M2 question - any help will be much appreciated watch

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1. Hi there,

It is question 2 part (ii) from the following past paper. I get that its the final kinetic energy but don't get why they equate it to the work done of one weight by the other. also, why is the mass 50kg instead of 25kg.

http://www.mei.org.uk/files/papers/m209ju_jk32.pdf

It would be grateful if someone could help me on this

2. (Original post by H4SS4N4TOR)
Hi there,

It is question 2 part (ii) from the following past paper. I get that its the final kinetic energy but don't get why they equate it to the work done of one weight by the other. also, why is the mass 50kg instead of 25kg.

http://www.mei.org.uk/files/papers/m209ju_jk32.pdf

It would be grateful if someone could help me on this

I would think of it as gain in KE = loss in PE (rather than talking about work)
All 3 particles are now moving with speed 1.5 which is why there is a 50 in the KE term.

With regards to the PE, B is moving down so loses PE of 20gx while A moves up and gains PE of 5gx, so overall loss is 20gx - 5gx.

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