*Q : Why a tennis ball bounces higher on hills than in planes ?*

Sol. Let u be the velocity of the tennis ball with which it bounces at a place , where acceleration due to gravity is g’ . The ball will go up till its velocity becomes zero . If h is the height up to which the ball rises up at a place , then initial K.E. of the ball is equal to final P.E. of the ball at highest point .

(1/2)mv^{2} = mg’h

h = u^{2}/2g’

As acceleration due to gravity (g’)on hill is less than that on the surface of earth (due to altitude effect ), so the ball will bounce higher on hills than on planes .