Which statement best explains why the sun is a star?
a. it's a huge ball of gas.
b. the planets all orbit it.
c. it's in the center of the solar system.
d. it creates its own energy through nuclear fusion.

Two masses are connected by a rope that hangs over a pulley as shown below. the pulley is a uniform cylinder of radius 푅=0.381meters and mass 푀=3.1푘푔. initially 푚"is on the ground and 푚#rests 2.5 meters above the ground. if the system is released, use conservation of energy to determine the speed of 푚#just before it strikes the ground. assume the pulley bearing is frictionless.