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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

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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