Question

A man with mass 81 kg lies on the floor. What is the normal force on the man?

A. 855 N
B. 794 N
C. 713 N
D. 820 N

Answer 1

Forces come in pairs, so the force of gravity (9.8 N) with the mans weight (794N) on the earth is counteracted with the normal force ( the force of the earth back on the man) which is the same

Answer 2

`F=m\cdot g\ \ \ \ \wedge\ \ \ \ g\approx9.8\ m/s^2\\ \\F\approx81\ kg\cdot9.8\ m/s^2=793.8\ (kg\cdot m)/(s^2) \approx794\ N\ \ \ \Rightarrow\ \ \ Ans.\ B`