Normal (N) and gravity force (W)
assume g = 10 m/s²
a. N = W = m₁.g = 3 x 10 = 10 N
b. W = m₂.g = 1.5 x 10 = 15 N
c. N = (m₁+m₂)g = 4.5 x 10 = 45 N
