# OCR A Level: Mechanics 2 - Projectile Motion [January 2012 Q7]

**Classical Mechanics**Level pending

A particle \(P\) is projected horizontally with speed \(15 \text{ms}^{−1}\) from the top of a vertical cliff. At the same instant a particle \(Q\) is projected from the bottom of the cliff, with speed \(25 \text{ms}^{−1}\) at an angle of \(θ°\) above the horizontal. \(P\) and \(Q\) move in the same vertical plane. The height of the cliff is \(60 \text{m}\) and the ground at the bottom of the cliff is horizontal.

\((\text{i})\) Given that the particles hit the ground simultaneously, find the value of \(θ\) and find also the distance between the points of impact with the ground.

\((\text{ii})\) Given instead that the particles collide, find the value of \(θ\), and determine whether \(Q\) is rising or falling immediately before this collision.

**Input the value of \(θ\) from part \((\text{ii})\) as your answer, correct to 3 significant figures.**

###### There are **6** marks available for part (i) and **9** marks for part (ii).

###### In total, this question is worth **20.8%** of all available marks in the paper.

###### This is part of the set OCR A Level Problems.

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