1) Is work done by a force only when force and displacement are parallel to each other?
2) A man is lifting a body vertically upward? What are the forces acting on the body? What is the sign of work done by these forces?
111)no...
if it is in another direction the horizontal component i.e. Fcosθ is applied.
2)1,Gravitation 2,force exerted by the man on the weight(i.e.the reaction force) denoted by R.,3)if it is inmotion..then the friction of the air.(denoted by μ)
311)No.
Not always since work done = F*s*cos O (o=theta or angle of elevation)
2)Gravitational force
Air friction
111.) No !
The net force on any type of a surfaces like inclined or plane = FScosθ