Give the magnitude and direction of the net force acting on a stone of mass 0.1 kg, (a) just after it is dropped from the window of a stationary train, (b) just after it is dropped from the window of a train running at a constant velocity of 36 km/h, (c ) just after it is dropped from the window of a train accelerating with `1 m s^(-2)`, (d) lying on the floor of a train which is accelerating with `1 m s^(-2)` , the stone being at rest relative to the train. Neglect air resistance throughout.

Explanation

(a) 1 N vertically downwards (b) same as in (a) (c) same as in (a), force at an instant depends on the situation at that instant, not on history. (d) 0.1 N in the direction of motion of the train.