Question

Consider an automobile moving at v mph that skids d feet after its brakes lock. Calculate how far it would skid if it was moving at 2v and the brakes were locked.

Answer 1

Assuming the same acceleration in both cases, first, find the deceleration:

$$a=v^2/(2d_v).$$

Now, find the distance upon the same acceleration but a greater speed:

$$d_{2v}=(2v)^2/(2a)=4v^2/(v^2/d)=4d_v.$$