(Challenge Problem) A worker pulls a 40.0-kg crate with a rope at the 30.0o angle to the horizontal. The coefficient of sliding friction between the crate and the floor is 0.55. If he moves the crate
with a constant velocity a distance of 7.00 m, how much work does the worker do on the crate?
(hint: make 2 equations for 2 unknowns)

According to an observer on earth, planet x is stationary. maria and samir depart earth on their spaceships at the same time, each flying at 0.5c. maria flies toward planet x and samir flies in the opposite direction. according to maria, her voyage to planet x takes 9 years. how many years does maria's voyage take according to samir?