A man pushes a 200 N crate up a frictionless incline with a slope of 20 degrees. The crate is raised by 4 m as

Question

shown. Assuming the crate moves at constant speed, what is the work done by the man?.

I know Work = Force x Displacement. The answer is 800 N. Why is the displacement 4 m and not the hypotenuse of the ramp (4/sin20)?

Answer 1

The increase in gravitational potential energy
= m g h
where h is the HEIGHT change, the increase in distance from the center of the earth.
Work = distance times force IN THE DIRECTION OF MOTION
200 * 4 = 800 Joules
alternatively force component up slope * 4/sin 20
= 200 sin 20 * 4/sin 20 = 800 :)