The formula r = 2√𝟓𝑳can be used to approximate the speed r, in miles per hour, of a
car that has left a skid mark of L, in feet.
How far will a car skid at 50 mph? at 70 mph?
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