Problem 7.65 Part A At an accident scene on a level road, investigators measure

Question

Problem 7.65 Part A At an accident scene on a level road, investigators measure a car's skid mark to be 98 Im long. It was a rainy day and the coefficient of friction was estimated to be 0.30 Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes Express your answer using two significant figures OF m/s Submit My Answers Give Up Part B Why does the car's mass not matter? Essay answers are limited to about 500 words (3800 characters maximum, including spaces). 3800 Character(s) remaining Submit My Answers Give Up

Explanation / Answer

given,

distance = 98 m

coefficient of friction = 0.3

friction force after applying brakes = k * mg

force = ma

so,

ma = k * mg

a = k * g

by third equation of motion

v^2 = u^2 + 2as

since final velocity is 0

0 = u^2 - 2 * (k * g) * s

0 = u^2 - 2 * (0.3 * 9.8) * 98

u = 24 m/s

speed of car when brakes were applied = 24 m/s

mass of car doesn't matters because initial speed depends on acceleration and distance covered and acceleration is dependent on force not mass as we saw while calculating the acceleration

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