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Q.
In which of the following cases the net force acting on the body is not zero?
Laws of Motion
Solution:
As the rain drop is falling down with a constant speed, its acceleration, $a = 0$. Hence, net force on the drop $= ma = 0$. As the cork is floating on the surface of water, its weight is balanced by the upthrust. Hence, net force on the cork is zero
The force exerted by the engine is balanced by the friction due to rough road. As the car is moving with constant velocity, its acceleration $a = 0$ Hence, net force on the car, $F = ma = 0$
Whenever a body is thrown vertically upwards gravitational pull of earth gives it a uniform acceleration, $a = g$ in downward direction
Hence, net force on the pebble $=mg : 0.05 \times 10=0.5\,N$ vertically downwards