# physics

A car starts from rest and travels for 4.1 s with a uniform acceleration of +1.4 m/s2. The driver then applies the brakes, causing a uniform acceleration of -1.8 m/s2. The breaks are applied for 1.80 s.

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1. I guess you want the total distance. Since v = at and s = vt + 1/2 at^2,

s = (1/2)(1.4)(4.1)^2 + (4.1)(1.4)(1.8) + (1/2)(-1.8)(1.8)^2 = 19.18 m

final velocity is

v = 1.4*4.1 + (-1.8)*1.8 = 2.5 m/s

average speed is 19.18m/(4.1+1.8)s = 3.25 m/s

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