Problems: Work 2 of the following 3 problems. CLEARLY indicate which problem you

Question

Problems: Work 2 of the following 3 problems. CLEARLY indicate which problem you wish to omit by drawing a large X across the problem. If you fail to indicate which problem you choose to omit, I will omit the last problem for you. 1) A car travelling at 38.5 m/s hits a patch of ice and then starts to brake. On the ice patch which is 25.0 m long, the car decelerates at a rate of 1.25 m/s. The car continues to brake on the dry pavement (after the ice) where the deceleration is 8.40 m/s a) what is the velocity of the car when it leaves the icy portion of the road? b) How much time did it take the car to traverse the ice? c) How far on the dry pavement does the car travel before coming to a complete stop? d) What is the total time that it takes the car to come to a stop?

Explanation / Answer

a

by equation of motion

v2 = u2 + 2as

v2 = 38.5*38.5 - 2*1.25*25

v = 37.68 m/s-2

b

by equation of motion

v = u + at

37.68 = 38.5 - 1.25t

t = 0.656 s

c

by equation of motion

v2 = u2 + 2as

0= 37.68*37.68 - 2*1.25*s

s = 567.912 m

d

v = u + at

0 = 37.68 - 1.25t

t = 30.144 s

total time = 0.656 + 30.144 = 30.8 s

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