vf2 = vi2 + 2a ∆x vf2 - vi2 2a (0 m/s)2 – (26.8 m/s)2 = ∆x 2(-3m/s2) -718.24 - 6 120 m You are driving at 26.8 m/s approaching a traffic light. It turns yellow. You slow down at a rate of -3m/s2 How far do you travel until you stop? = ∆x = ∆x Given: vi = 26.8m/s a = -3 m/s2 vf = 0 m/s ∆x =? = ∆x = ∆x

vf = vi + at vf - vi a (0 m/s) – (26.8 m/s) = t -3m/s2 9 s = t = t You are driving at 26.8 m/s approaching a traffic light. It turns yellow. You slow down at a rate of -3m/s2 How much time passes? = t = t Given: vi = 26.8m/s a = -3 m/s2 vf = 0 m/s t =?

You are driving at 26. 8 m/s approaching a traffic light You are driving at 26.8 m/s approaching a traffic light. It turns yellow. You slow down at a rate of -3m/s2 If you are 125 m away from the light when you hit the brakes, will you stop ahead of the light, precisely at the light, or will you go beyond the light? You will stop 5 m before the light. 125 m – your stopping distance 125 m – 120 m = 5 m 120 meters 5 m 125 meters

You are driving at 26. 8 m/s approaching a traffic light You are driving at 26.8 m/s approaching a traffic light. It turns yellow. You slow down at a rate of -3m/s2 If the light is yellow for 2 seconds before it turns red, did you make the correct decision to slow down? Why or why not? Yes, you made the correct decision. It took 9 seconds to stop and the light turned from yellow to red after 2 seconds. Therefore the light was already red for 7 seconds by the time you stopped 120 meters 5 m 125 meters

= a = a Given: vi = 26.8m/s a = ? = a vf = ? ∆x = 125 m ∆t = 2 s ∆x = vit + ½at2 ∆x - vit ½(t2) 125 m – (26.8 m/s)(2 s) ½ (2 s)2 71.4 2 35.7 m/s2 = a You are driving at 26.8 m/s approaching a traffic light. It turns yellow. You slow down at a rate of -3m/s2 Can you figure out what you would have to do to ‘make the light’, i.e. get through it in two seconds and being 125 m away? = a = a Given: vi = 26.8m/s a = ? vf = ? ∆x = 125 m ∆t = 2 s = a

CRAZY Given: vi = 26.8m/s a = 35.7 m/s2 vf = ? ∆x = 125 m ∆t = 2 s vf2 = vi2 + 2a ∆x vf2 = (26.8 m/s)2 + 2(35.7 m/s2)(125m) vf2 = 9643 vf = 9643 vf = 98 m/s or 216 mph You are driving at 26.8 m/s approaching a traffic light. It turns yellow. You slow down at a rate of -3m/s2 Can you figure out what you would have to do to ‘make the light’, i.e. get through it in two seconds and being 125 m away? Given: vi = 26.8m/s a = 35.7 m/s2 vf = ? ∆x = 125 m ∆t = 2 s CRAZY