(a) What is meant by mechanical energy ? State its two forms. State the law of conservation of energy. Give an example in which we observe a continuous change of one form of energy into another and vice-versa.

(b) Calculate the amount of work required to stop a car of 1000 kg moving with a,speed of 72 km h^-2.

(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

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