The formula r = 2√𝟓𝑳can be used to approximate the speed r, in miles per hour, of a

Question

car that has left a skid mark of L, in feet.
How far will a car skid at 50 mph? at 70 mph?

Answer 1

r = 2 √5 L

Square both sides

r² = 2² ∙ 5 L

r² = 4 ∙ 5 L

r² = 20 L

Divide both sides by 20

r² / 20 = L

L = r² / 20

r = 50 mph

L = 50² / 20 = 2500 / 20

L = 125 ft

r = 70 mph

L = 70² / 20 = 4900 / 20

L = 245 ft