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Question
Give the magnitude and direction of the net force acting on a stone of mass 0.1 kg, just after it is dropped from the window of a train running at a constant velocity of 36 km/h. Neglect air resistance.
Solution
As the train travels at a constant speed, it has no acceleration. Thus, no forces resulting from the train's motion affect the stone. Therefore, force on the stone F = weight of stone = mg = 0.1 × 10 = 1.0 N
This force acts vertically downward.
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