This part of the problem applies to any road surface, so the value of h is not known. Suppose you are driving at 70 miles per hour but, because of approaching darkness, you wish to slow to a speed that will cut your emergency stopping distance in half. What should your new speed be?

  v₀ = 49.5 miles / h

Explanation:

We can solve this exercise with kinematics in one dimension

        v² = v₀² - 2 a d

let's apply this equation to the initial data, the fine velocity zero

       0 = v₀² - 2 a d

       a = v₀² / 2d

in the second case the distance is half (d´ = ½ d), the acceleration of the vehicle is the same, we look for the initial speed

      0 = v₀´² - 2 a d´

      v₀´² = 2 a d = 2 (v₀² / 2d) d´

      v₀´ = v₀ √ 1/2

let's calculate

       v₀´ = 70 ra 0.5

      v₀ = 49.5 miles / h

0.55x745.7j and a calculator

what is the speed of a softball that travels 20m in 2secs

speed = 20/2 = 10 m/s