SHOW ALL WORK PLEASE Imagine an aspiring young lab coordinator at age 17 getting
ID: 1771709 • Letter: S
Question
SHOW ALL WORK PLEASE Imagine an aspiring young lab coordinator at age 17 getting a rusty ’66 pickup ready for a Styx concert when another teenager comes speeding around a corner who dings hissweet ride halfway down the block. The offending vehicle locked its brakes and left an 88 ft long skid mark (as measured by police) on the dry asphalt. As the responding officer on the scene, use the following information from your physics folder (cops actually have these) to determine whether or not to add a ticket for speeding in a 30 mph zone in addition to reckless driving. Cite evidence. Coefficient of Friction between commercial tires and various road surfaces and conditions Dry Wet Concrete 0.68 0.58 Asphalt 0.67 0.53
Explanation / Answer
coefficient of friction for dry asphalt = 0.67
length of skid mark = 88 ft = 26.82 m
30mph = 13.41 m/s
Let 'u' be the initial speed of the car
Applying principle of energy conservation,
KEi - (work done by friction) = KEf
(1/2)mu2 - mg*s = 0
=> u = (2gs)
=> u = (2*0.67*9.81*26.82)
=> u = 18.78 m/s
We can see that 'u' is well above the speed limit of 13.41m/s(30 mph)
Therefore, the officer should add a ticket for speeding
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