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File Edit View ools Help CI sign In-mycl CSU Chan... P sign In Masteringphysics WeBWork csuci-math 151 PHYS 100-01 Spring 2017 CSUCI DavidNelson HW 02 C Exercise 2.58 C Exercise 2.58 Part A An automobile is traveling on a long, straight What was the car's speed just after leaving the icy portion of the road? highway at a steady 76.0 mi/h when the driver sees a wreck 180 m ahead. At that instant, she applies the brakes (ignore reaction time). Between her and the wreck are two different surfaces. First there is 130 m of ice, where the deceleration is only 1.20 m/s From then on, it is dry concrete, m/s E 29017 where the deceleration is a more normal 7.10 Submit My Answers Give Up incorrect; Try Again 8 attempts remaining Part B What is the total distance her car travels before it comes to a stop? Signed in as Lau

Explanation / Answer

initial speed is Vo = 76 mi/h = 33.97 m/sec

distance travelled on ice is S_ice = 130 m

accelaration is a = -1.2 m/s^2

using V^2 - Vo^2 = 2*a*S_ice

V^2 - 33.97^2 = -2*1.2*130

V = 29 m/sec is the answer for a)

b) on dry concrete

Vo = 29 m/sec

V = 0 m/s

a = -7.1 m/s^2

then using

V^2 - Vo^2 = 2*a*S

0^2 - 29^2 = -2*7.1*S = 59.22 m

so total distance travelled before stopping is 130+59.22 = 189.22 m

C) time taken on ice is t1

using V = Vo + (a*t1)

29 = 33.97-(1.2*t1)

t1 = 4.14 sec

time taken on dry concrete is

V = Vo +(a*t2)

0 = 29-(7.1*t2)

t2 = 4.08 sec

total time taken is t1+t2 = 4.14+4.08 = 8.22 sec

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