Question

You're approaching an intersection at 50 km/h (13.9 m/s ). You see the light turn yellow when you're 35 m from the intersection. Assume a reaction time of 0.6 s before braking begins and a braking acceleration of -3.0 m/s2.

A) will you be able to stop at before the intersection?

B) The yellow light stays on for 3.4 s before turning red. If you continue at 50 km/h without braking, will you make it through the 9.5-m-wide intersection before the light turns red?

Answer 1

d = 13.9 * .6 + (13.9/2)t
because average speed during deacceleration = half the original speed

time to stop during acceleration is t:
v = Vi + a t in general
so
0 = 13.9 - 3 t
t = 13.9/3
so in the end
d=13.9*.6 + (13.9/2)(13.9/3)

part b
will you go 35+9.5 meters in time?
what is 13.9 m/s * 3.4 seconds?