In his Principia Mathematica Newton expressed his third law of motion as “to every action there is always opposed an equal reaction”. State what Newton meant by this law. (1) (b) A book is released from rest and falls towards the surface of Earth. Discuss how the conservation of momentum applies to the Earth-book system. (3) Worksheet Work, Energy, Power & Momentum 5 (c) A large swinging ball is used to drive a horizontal iron spike into a vertical wall. The centre of the ball falls through a vertical height of 1.6 m before striking the spike in the position shown. The mass of the ball is 3.5 kg and the mass of the spike is 0.80 kg. Immediately after striking the spike, the ball and spike move together. Show that the (i) speed of the ball on striking the spike is 5.6 m s–1 .