Let the block of mass #m# be projected along the smooth inclined plane having angle of inclination #alpha# 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=ssinalpha#
Now retardation of the block along the inclined plane is #gsinalpha#
So #s=vt-1/2gsinalphat^2#
And
#h=ssinalpha#
#=>h=vsinalphat-1/2gsin^2alphat^2#
So potential enrgy of the block at time t will be
#E_p(t)=mgh#
#=vmgsinalphat-1/2mg^2sin^2alphat^2#
#=at-bt^2#
Where #a and b# are constants as #v,m,g and alpha# are constants.
So a plot of #E_p(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.
