Amotorist is traveling at 20 m/s. he is 60 m from a stoplight when he sees it turn yellow. is reaction time, before stepping on the brake, is 0.50 s. what steady acceleration (slowing down) while braking will bring him to a stop right at the light?

V₀ = V₁ + 2ax
V₀ = final velocity which is 0 m/s
V₁ = initial velocity which is 20 m/s
x = distance which is 60-(0.5 x 20) =50m
     this is because his reaction time is 0.5 sec so he traveled 10m before stepping on the break paddle.

a= (V₀-V₁) / 2x
  = (0-20) / 2*50
  = -0.2m/s
the negative is because it is a deceleration speed hence it is 0.2m/s