Question

You're driving down the highway late one night at 20 m/s when a deer steps onto the road 38 m in front of you.Your reaction time before stepping on the brakes is 0.50 s ,and the maximum deceleration of your car is 10 m/s^2 what is the maximum speed you could have and still not hit the deer

Answer 1

Consider the motion of the car before brakes are applied:

v₀ = maximum initial velocity of the car before the brakes are applied

t = reaction time = 0.50 s

x₀ = distance traveled by the car before brakes are applied

since car moves at constant speed before brakes are applied

Using the equation

x₀ = v₀ t

x₀ = v₀  (0.50)

Consider the motion after brakes are applied :

v₀ = initial velocity of the car before the brakes are applied

a = acceleration = - 10 m/s²

v = final velocity of the car after it comes to stop = 0 m/s

x = stopping distance = initial distance - distance traveled before applying the brakes = 38 - x₀ = 38 - v₀  (0.50)

Using the equation

v² = v²₀ + 2 a x

inserting the values

0² = v²₀ + 2 (- 10) (38 - v₀  (0.50))

v²₀ = 20 (38 - v₀  (0.50))

v₀ = 23 m/s