A disk and a sphere are released simultaneously at the top of an inclined plane. They roll down without slipping. Which will reach the bottom first?
a. the one of smallest diameter
b. the one of greatest mass
c. the sphere
d. they will reach bottom at same time
Answer is d. There are only two forces that have influence on the motion of the both disk and sphere. Those are gravity and friction forces. They both the same for sphere and disk - the gravity force does not depend on mass and friction force is the same because disk and sphere are moving in the same manner - they are rolling down. so, they will move with the same speed