PHYS 191 Spring\'18 Exam 1-A Name Keep at least 5 significant figures when perfo

Question

PHYS 191 Spring'18 Exam 1-A Name Keep at least 5 significant figures when performine the calculations Write your answers with 3 significant figures in the blanks provided. Show units 1. The minimum time for the duration of yellow light on a traffic light is 3.0 seconds You are approaching a traffic light at 40 mph. When you are 45 m away from the light, iIt turns vellow you decide to accelerate, and are traveling at 50 mph at the moment you reach the Still accelerating you make it to the other side of the intersection just as the ltight turns red. o ight. How wide is the intersectioni? for partial credit submit answers to questions below i) What is your initial speed in metric units? ii)What is your speed when you reach the intersection?, ii) How much time does it take you to reach the beginning of intersection? iv) What is the magnitude of your acceleration as you do so? v) What additional distance will you drive with this acceleration before the light turns red? A balloonist, riding in the basket of ot air balloon that is rising vertically with a constant leases a sandbag when the balloonm above the ground. The bag hits the ground 4 se ote: the bag is NOT released from i ince the balloon is rising at is the bag's speed when it hits t quest

Explanation / Answer

1. v0 = 40 x 1609 m / 3600 s = 17.88 m/s

v = 50 x 1609 m / 3600 s = 22.35 m/s

d = 45 m

Applying vf^2 - vi^2 = 2 a d

22.35^2 - 17.88^2 = 2(a)(45)

a = 2 m/s^2

vf = vi + a t

22.35 = 17.88 + 2 t1

t1 = 2.235 sec

time remainig = 3 - t1 = 0.765 sec  

d = vi t + a t^2 /2

d = (22.35 x 0.765) + (2 x 0.765^2 / 2) = 17.68 m ......Ans ( Width of intersection)

(i) vi = 17.88 m/s

(ii) v = 22.35 m/s

(iii) t1 = 2.235 sec  

(iv) a = 2 m/s^2

(v) 17.68 m

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