Question

You are driving to the grocery store at 20 m/s . You are 110m from an intersection when the traffic light turns red. Assume that your reaction time is 0.50s and that your car brakes with constant acceleration.
_ How far are you from the intersection when you begin to apply the brakes?
_ What acceleration will bring you to rest right at the intersection
_ How long does it take you to stop after the light changes.?

Answer 1

v0 = 20m/s
D = dist from int. = 110 - v0 x 0.50
t0 = time to stop
final velocity must equal zero...
0 = v0 - a x t0
t0 = v0/a
D = v0 x t0 - a x t0^2/2
substitute for t0...
D = v0^2/a - a x (v0/a)^2/2
solve for a...

Answer 2

Thank you