An object is thrown straight up. Which of the following is true about the sign of work done by the gravitational force while the object moves up and then down
a)Work is positive on the way up, work is positive on the way down
b)Work is negative on the way up, work is negative on the way down
c)Work is negative on the way up, work is positive on the way down
d)Work is positive on the way up, work is negative on the way down