A motorist 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