Q. Suppose you are driving on the interstate at 85 mph when you see a highway patrol car parked up ahead. You apply your brakes, decelerating at a constant rate of 4 mph/sec until you're reduced your speed to 65 mph. You then maintain a constant speed of 65 mph. You pass the patrol car 15 seconds after you initially applied the brakes and are relieved that he doesn't pull out after you. How far away was the highway patrol car when you first saw it?(adsbygoogle = window.adsbygoogle || []).push({});

Ans. Two different situations to this problem,

1st situation,

we can find the time, it took to reduce the speed from 85 mph to 65 mph

t = (85mph - 65mph) / 4 m/s2

t = 5 seconds. ( Note: It decelarates in the first phase @ the rate of

4mph / sec.)

2nd Situation

Thereafter, it continues, at a constant rate of 65 mph.

Use constatnt acc. equation.

x - xo = vot + 1/2 at^2

Will vo be 65mph

and t = 10 seconds

a = -4 mph /sec

-----------------------------------

For the first situation, knowing the time t = 5 seconds,

we need to use

x - xo = vot + 1/2 at^2 again

Here, what would vo be?

t would be 5 seconds for sure.

I think 'a' would be 4mph /sec

Am I right with the variables.

Please help anybody

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# Homework Help: Highway Patrol Problem

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