Two boys with masses of 40 kg and 60 kg stand on a horizontal frictionless surface holding the ends of a light 10-m long rod.The boys pull themselves together along the rod.When they meet the 40-kg boy will have moved what distance?
A)4 m
B)5 m
C)6 m
D)10 m
E)need to know the forces they exert

Question

Quizplus · Accepted Answer

The 40-kg boy will have moved 6 m. This is because the center of mass of the system must remain constant if there are no external forces. The center of mass is closer to the heavier boy, so the lighter boy moves a greater distance. The distances moved are inversely proportional to their masses, so the 40-kg boy moves (40/(40+60))*10 = 4/10 of the distance, which is 6 m.

Two Boys with Masses of 40 Kg and 60 Kg