Question

A 20 kg box is pushed up a rough sloping ramp (30o relative to the incline) with a force of 300 N, parallel to the horizontal with constant speed. what is frictional force

Answer 1

Let's apply Newton's Second Law of Motion in projection on $x$-axis:

$$F_{p}-mgsin\theta-F_{fr}=0,$$ $$F_{fr}=F_{p}-mgsin\theta,$$ $$F_{fr}=300\ N-20\ kg\cdot9.8\ \dfrac{m}{s^2}\cdot sin30^{\circ}=202\ N.$$