Motion in a Straight Line

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+‌

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2

at2
We get y−h=−‌

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gt2⇒y=h−‌

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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).