A boy of mass 50 kg is standing on a weighing machine placed on the floor of a lift. The machine reads his weight in newton. What is the reading of the machine when the lift is stationary? Take g=9.8 ms−2
Mass of the boy, m=50 kg
Acceleration due to gravity, g=9.8 ms−2
Let the weighing machine exert a normal force N on the boy in vertically upward direction.
As the lift is stationary, acceleration of the boy is zero.
From second law of motion, N−mg=0⇒N=mg=50×9.8=490 N
The machine measures this normal force. Thus, the correct choice (c).