A stage crew member uses a pulley system to close the curtains on stage. If he does 620 Joules of work and the pulley system does 415 Joules of work, the efficiency of the pulley system is

Aheavy boy and a lightweight girl are balanced on a massless seesaw. the boy moves backward, increasing his distance from the pivot point. what happens to the seesaw? it is impossible to predict without knowing additional information. the side the boy is sitting on will tilt downward. the side the girl is sitting on will tilt downward. nothing; the seesaw will remain balanced.