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10 November, 23:39

A car starts from rest and travels for 7.0 seconds with auniform

acceleration of + 2.5 m/s^2. The driver then applies thebrakes,

causing a uniform acceleration of - 3.0 m/s^2. If the brakesare

applied for 2.0 seconds, how fast is the car going at the endof the

braking period, and how far has it gone?

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Answers (1)
  1. 11 November, 00:41
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    Answer

    given,

    initial speed = 0 m/s

    acceleration of + 2.5 m/s^2 for time 7 s.

    final velocity after 7 s

    using equation of motion

    v = u + a t

    v = 0 + 2.5 x 7

    v = 17.5 m/s

    after 7 sec

    Brake is applied, uniform acceleration = - 3.0 m/s^2

    time = 2 s

    speed of the car after 2 s

    initial velocity = 17.5 m/s

    Again using equation of motion

    v = u + a t

    v = 17.5 - 3 x 2

    v = 11.5 m/s

    distance the car has traveled when brake is applied

    v² = u² + 2 a s

    11.5² = 17.5² - 2 x 3 x s

    6 s = 174

    s = 29 m

    car has moved 29 m after application of the brake.
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