The line on the position time graph show the velocites of different vehicles which line represents a vehicle moving at constant velocity

For some mysterious reason, we can't see the graph.

On a position/time graph, constant velocity is represented by a straight line.  Depending on the velocity, the line may be sloping up, sloping down, or horizontal.  The only thing the line on the graph CAN't be is vertical.

i think it is non rem sleep

the first american roller coaster was the mauch chunk switchback railway, built in the mountains of pennsylvania in the mid-1800s. the track, originally built to send coal to a railway, was reconfigured as a "scenic tour."