sign of work done by gravity
sir, when the ball is going up then displacement is upward and the gravitational force is downward but what about the force which is given by the man when he is throwing the ball upward then the force and displacement will be in the same direction, without the force exerted by the man the ball cannot go upward then it should be positive rather than negative.Explain.
Since some gravity equations result in an object changing directions, there needs to be a convention as to which direction is positive and which is negative.
Due to the fact that the force of gravity is downward, it would only seem logical to define downward as a positive direction and upward as a negative direction in gravity equations.
Hence, in case of throwing a ball in the upward direction it is considered as negative rather positive.