. A ball of mass 2000 g is dropped from the top of a 200 cm high building. (g = 10 m/s2 ). (Assume potential energy at the ground level to be zero.) (a) What is the kinetic energy of the ball when it reaches the ground? (2) (b) What is the total mechanical energy of the ball when it reaches the ground?

SolutionThe sum of kinetic energy and potential energy is always constant.Potential energy at top= mghP.E =20001000kg×10×200100m=40 JoulesWhen it reaches on ground,all its P.E converts in K.E  So,K.E when ball reaches to ground = 40 J Total mechanical energy i.e.. the sum of kinetic energy and potential energy.Since potential energy is zero at ground so total mechanical energy = 40 J

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