Question

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?

Answer 1

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