The theory of relativity predicts that an object whose mass is z when it is at rest will appear heavier when moving at speeds near the speed of light. When the object is moving at speed v, its mass m is given by the following equation, where c is the speed of light.

m=z/sqrt(1-v^2/c^2)

(a) Find dm / dv.

(b) In terms of physics, what does dm / dv tell you?