# Velocity and Constant Acceleration

Two ships P and Q are moving along straight lines with constant velocities. Initially P is at a point O and the position vector of Q relative to O is (6i + 12j) km, where i and j are unit vectors directed due east and due north respectively. The ship P is moving with velocity 10j km h–1 and Q is moving with velocity (−8i + 6j) km h−1. At time t hours the position vectors of P and Q relative to O are p km and q km respectively. (a) (b) (c) Find p and q in terms of t. (3)

Calculate the distance of Q from P when t = 3.

(3)

Calculate the value of t when Q is due north of P.

(2) (Total 8 marks)

2.

A train starts from rest at a station A and moves along a straight horizontal track. For the first 10 s, the train moves with constant acceleration 1.2 m s–2. For the next 24 s it moves with constant acceleration 0.75 m s–2. It then moves with constant speed for T seconds. Finally it slows down with constant deceleration 3 m s–2 until it comes to rest at a station B. (a) (b) (c) Show that, 34 s after leaving A, the speed of the train is 30 m s–1. (3)

Sketch a speed-time graph to illustrate the motion of the train as it moves from A to B. (3)

Find the distance moved by the train during the first 34 s of its journey from A. (4)

The distance from A to B is 3 km. (d) Find the value of T.

(4) (Total 14 marks)

3.

Two cars A and B are moving in the same direction along a straight horizontal road. At time t = 0, they are side by side, passing a point O on the road. Car A travels at a constant speed of 30 m s–1. Car B passes O with a speed of 20 m s–1, and has constant acceleration of 4 m s–2. Find (a) (b) (c) the speed of B when it has travelled 78 m from O, (2)

the distance from O of A when B is 78 m from O,

(4)

the time when B overtakes A.

(5) (Total 11 marks)

4.

A post is driven into the ground by means of a blow from a pile-driver. The pile-driver falls from rest from a height of 1.6 m above the top of the post. (a) Show that...

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