Qualification > Math

Confusing M1 question

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XaM!!:
Two particles P and Q have mass 0.5 kg and m kg respectively, where m < 0.5. The particles are connected by a light inextensible string which passes over a smooth, fixed pulley. Initially P is 3.15 m above horizontal ground. The particles are released from rest

When P strikes the ground, P does not rebound and the string becomes slack. Particle Q then moves freely under gravity, without reaching the pulley, until the string becomes taut again.

e) Find the time between the instant when P strikes the ground and the instant when the string becomes taut again.

I got 6/7 s which is the right answer

But I was thinking when P hits the ground doesn't Q move up 3.15m and so i calculate the time for this and add it on to the time for the string going slack 

I've attached the question picture

astarmathsandphysics:
No cos the acceleration is not the same - anyway it says from when P hits the ground

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