When you see a traffic light turn red, you apply the brakes until you come to a

Question

When you see a traffic light turn red, you apply the brakes until you come to a stop. Suppose your initial speed was 12.3 m/s, and you come to rest in 35.8 m. How much time does this take? Assume constant deceleration. -12 points My Notes Ask Your A 27 pound meteorite struck a car, leaving a dent 20 cm deep in the trunk. If the meteorite struck the car with a speed of 530 m/s, what was the magnitude of its deceleration, assuming it to be constant? m/s2 0 12 points My Notes Ask Your Here's something you can try at home an experiment to measure your reaction time. Have a friend hold a ruler by one end, letting the other end hang down vertically. At the lower end, hold your thumb and index finger on either side of the ruler, ready to grip it. Have your friend release the ruler without warning. Catch it as quickly as you can. If you catch the ruler 5.8 cm (~2.3 inches) from the lower end, what is your reaction time?

Explanation / Answer

vi = 12.3 m/s

vf = 0

and d = 35.8 m

vf^2 - vi^2 = 2 a d

0^2 - 12.3^2 = 2(a)(35.8)

a = -2.11 m/s^2

vf = vi + a t

0 = 12.3 - 2.11 t

t = 5.82 sec

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vf^2 - vi^2 = 2 a d

0^2 - 530^2 = 2(a)(0.20)

a = - 7.02 x 10^5 m/s^2

Ans: 7.02 x 10^5 m/s^2

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d = v0 t + a t^2 / 2

0.058 = 0 + 9.8 t^2 /2

t = 0.11 sec

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