physics

A car starts from rest and travels for 5.0 s with a uniform acceleration of +2.5 m/s2. The driver then applies the brakes, causing a uniform negative acceleration of -3.0 m/s2. If the brakes are applied for 2.0 s, how fast is the car going at the end of the braking period, and how far has it gone?

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  1. V1 = a*t = 2.5 * 5 = 7.5 m/s.

    a. V2 = V1 + a*t = 7.5 -(3 * 2) = 1.5 m/s. After the braking period.

    b. d1 = 0.5a*t^2 = 0.5*2.5*5^2 = 31.25 m.

    d2 = V1*t + 0.5a*t^2.
    d2 = 7.5*2 - 0.5*3*2^2 = 9 m.

    d = d1+d2 = 31.25 + 9 = 40.25 m.

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