Understanding the Concepts

* Force of Gravity: The Earth exerts a downward force on the boy due to gravity. This force is calculated using the equation:

* Force (F) = mass (m) * acceleration due to gravity (g)

* g = 9.8 m/s² (approximately)

* Normal Force: The floor exerts an upward force on the boy, equal in magnitude and opposite in direction to the force of gravity. This is known as the normal force.

Calculations

1. Calculate the force of gravity:

* F = m * g

* F = 45 kg * 9.8 m/s²

* F = 441 N (Newtons)

2. The normal force is equal and opposite to the force of gravity:

* Normal Force = 441 N

Answer: The upward force of the floor against the boy's feet is 441 Newtons.