Circular disc, A rolls around another circular disc, B (without slippi

A tricky question.

If the radius of A is x, then radius of B = 4x

Circumference of B = \(2\pi * 4x\) = \(8 \pi x\) is the distance that has to be traveled by the smaller circle of circumference \(2 \pi x\).

Therefore the number of revolutions should be \(\frac{8 \pi x}{2 \pi x} = 4\)


If this were a straight road instead of a circle, this answer would have been correct.

Since the disc is moving around the circle, there is a second movement happening with the revolution, which is a rotation.

One rotation of the smaller disc from the staring point to the end point is 1 extra revolution.


In general the total number of revolutions of a circular disc around another circle = n + 1, where n is the number of revolutions found by dividing the larger circumference by the smaller circumference the +1 accounts for the revolution due to the 1 rotation.


The Correct answer is Option C

Arun Kumar