Laws of motion

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.