In part (b) I had equated kinetic energy of mass Q to it's potential energy to see the height it would reach i.e. 1/2mv^2=mgh. In the marking scheme there was another 1/2mv^2 on the right (mgh) side of the equation. However the question stated that the string went slack at the instant Q reached max height indicating it's velocity at this point was 0. Wondering where that second 1/2mv^2 they got came from as it changed the answer significantly. Any help would be great if any of you have done the paper. Cheers!