The man rolls the cupboard at a steady speed from the lorry to the house. The friction force in the wheels is 40 N. State the force with which the man has to push.

40N

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

+15-35=-20

going in opposite directions