In a differential mechanism, two equal sized bevel wheels A and B are keyed to the two halves of the rear axle of a motor car. The car follows a curved path. Which one of the following statements is correct?
The wheels A and B will revole at different speeds and the casing will revolve at a speed which is equal to the
(a) difference of speeds of A and B
(b) arithmetic mean of speeds of A and B
(c) geometric mean of speeds of A and B
(d) harmonic mean of speeds of A and B