question_answer

A boy having a mass of 60 kg, holds in hand a school bag of weight 40 N. With what force the floor will push up on his feet ? \[\text{(g }=\text{ 1}0\text{ m}/{{\text{s}}^{\text{2}}})\]

A)  100 N                                   

B)  600 N

C)  640 N                                   

D)  64 N

Correct Answer: C

Solution :

                 Total force acting on boy bag system, is given by                                 F = weight of boy + weight of bag                 F = 60 g + 40N \[\Rightarrow \]               F = 60 \[\times \] 10 + 40 = 640N From Newtons third law, to every action there is an equal and opposite reaction. Therefore, the floor will push on his feet with a force of 640 N.