the 4th part...I don't really understand what they're asking for :S
When A strikes the ground, B continues to rise against gravity until it reaches its maximum point where
v = 0. Then B starts to descend due to its weight. String becomes taut again when B reaches the level it started to rise against gravity, i.e at the time when A touched the ground earlier.
In other words, you need to find the time taken the particle B takes to reach its maximum height as from when A strikes the ground. Multiply it by
2 since for the string to become taut again, B covers twice this distance(once upwards and then downwards) and during the same time.
For the required solution you need to add the value you obtain to your answer in part(ii)
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Hope it helps
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If you still cannot do it, let me know
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