Why does an object have a different weight on the moon than it does on earth

a. objects move slowly on the moon

b. the earth and the moon have different values for acceleration due to gravity

c. everything is weightless in space

d. there is no air in the moon so objects her lighter

A1-lb collar is attached to a spring and slides without friction along a circular rod in a vertical plane. the spring has an undeformed length of 5 in. and a constant k =25 lb/ft. knowing that the collar is released from being held at a determine, the speed of the collar and the normal force between the collar and the rod as the collar passes through b.