A Boy whose mass is 75 kg holds in his hands a bag weighning 40 N .with what force does the floor push up on his feet.
EXPLAIN WITH FIGURE
Weight of the boy, W = (75 x 9.8) N = 735N
Weight of the bag, W' = 40 N
Total force exerted on the ground, F = W + W' = 775N
The force exerted by the ground on the boy is 775N.
This is due to the third law of motion which stated that every action, there is always an equal and opposite reaction that acts on different bodies.
Here the boy and the bag form one system acting on the ground with force F and the ground exerts an equal but opposite force F on the system.