For downward motion : v=−gt The velocity of the rubber ball increases in downward direction and we get a straight line between v and t with a negative slope. Also applying y−y0=ut+
1
2
at2 We get y−h=−
1
2
gt2⇒y=h−
1
2
gt2 The graph between y and t is a parabola with y=h at t=0. As time increases y decreases. For upward motion : The ball suffer elastic collision with the horizontal elastic plate therefore the direction of velocity is reversed and the magnitude remains the same. Here v=u−gt where u is the velocity just after collision. As t increases, v decreases. We get a straight line between v and t with negative slope. Also y=ut−
1
2
gt2 All these characteristics are represented by graph (B).