Answer:
40N
Step-by-step explanation:
Using the newton's second law of motion
\sum Fx = max
Fm - Ff = max
Fm is the applied force
Ff is the frictional force
m is the mas of the cupboard
ax is the acceleration
Since the speed from the lorry is steady, ax = 0m/s^2
Also Ff = 40N
Substitute into the formula;
Fm - 40 = m(0)
Fm - 40 = 0
Add 40 to both sides
Fm - 40 + 40 = 0 + 40
Fm = 40N
Hence the force with which the man applied to push is 40N