suscription problem about 2 hours ago

suscription button is not avilable ....how can i suscribe to this site to watch all video....

Physic about 5 months ago

A man in a train moving with a constant velocity drops a ball on the plateform .The path of the ball as seen by an observer standing at the plateform is  (a) St.line      (b) Circle      (c) Parabola     (d) Hyperbola