A ball is thrown straight up. What can be said about the sign of work done by the force exerted by gravity while the ball moves up and then down?
A) Positive as the ball travels up, and positive as the ball travels down
B) Zero as the ball travels up, and zero as the ball travels down
C) Negative as the ball travels up, and negative as the ball travels down
D) Positive as the ball travels up, and negative as the ball travels down
E) Negative 'as the ball travels up, and positive as the ball travels down