Let the block of mass m be projected along the smooth inclined plane having angle of inclination α with the horizontal and it moves distance s along the inclined plane in time t. During this time if it achieves a vertical height h,then h=ssinα
Now retardation of the block along the inclined plane is gsinα
So s=vt−12gsinαt2
And
h=ssinα
⇒h=vsinαt−12gsin2αt2
So potential enrgy of the block at time t will be
Ep(t)=mgh
=vmgsinαt−12mg2sin2αt2
=at−bt2
Where aandb are constants as v,m,gandα are constants.
So a plot of Ep(t) v/s t will be a parabola for the upward and downward movement of the block along the inclined plane.
So option (1) will be the answer.