(a) It is the sum of KE and PE of an object. It states that energy can neither be created nor be destroyed. We observe a continuous change in energy in a simple pendulum and its explanation. At the mean position, the energy is wholly kinetic while at the extreme position it is wholly potential. As the pendulum oscillates its energy continuously changes between kinetic and potential.
(b) Given m = 1000 kg,
u = 72 km h^-1 = 20 m s^-1, v = 0
Work done = Change in kinetic energy = 1/2 m (v^2 - u^2) = % x 1000 x (0^2 - 20^2)
= - 200000 J = - 2 x 10^5 J