# Math Help - directly proportional

1. ## directly proportional

The distance required for a car to stop is directly proportional to the square of its velocity. If a car can stop in 112.5 meters at 15 km per hour, how many meters are needed to stop at 25 kilometers per hour?

2. $d_1 = kv_1^2$ where k is a non-zero constant.

$d_2 = kv_2^2$

If you divide the first equation into the second one you can eliminate k

$\dfrac{d_2}{d_1} = \dfrac{kv_2^2}{kv_1^2} = \dfrac{v_2^2}{v_1^2}$

Solve for $d_2$ since everything else is given