a) The second Newton's law states that (The force is defined as the change rate of the quantity of motion , it means the force is the multiplication of the mass (m) and the acceleration(a))
[tex]F=ma[/tex]
Then, we can calculate the acceleration as:
[tex]a=\frac{F}{m}=\frac{20}{40}=0.5 m/s^2[/tex]
b) The normal force according to the third Newton's law which states that (For every action, there is an reaction has the same amplitude with opposite direction), is equal to the gravitational force with the opposite direction
Taking the accleration according to gravity is 9.8 [tex]m/s^2[/tex]
[tex]F_{g}=mg=40*9.8=392N[/tex]
Then, the normal force equals to 392N
