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Motion in 1 dimension easy question?

  1. Sep 24, 2011 #1
    a car starts from rest travels for 5.0s with a uniform acceleration of + 1.5m/s^2. The driver then applies the brakes, causing uniform acceleration of -2.0m/s^2. If the brakes are applies for 3.0s (a) how fast is the car going atthe end of the braking period and b how far has it gone

    I have already done part a and i have the answers for both parts i just dont know the steps in approaching part b
    the answer to b is 32.2m
    please help! thank you :D
     
  2. jcsd
  3. Sep 24, 2011 #2
    When it's speeding up, it starts at 0 m/s and after the speedup is at 7.5 m/s. That's an average of 3.75 m/s for 5 seconds, so the distance traveled during this part is 18.75 m.

    When it begins to brake, it's going at 7.5 m/s, and then after the braking is at 1.5 m/s. That's an average of 4.5 m/s during this period of 3 seconds, so during the braking it moves 13.5 meters.

    The sum is 32.25 meters.
     
  4. Sep 24, 2011 #3
    but what equation did you use?
     
  5. Sep 24, 2011 #4
    x = t (v_i + v_f) / 2
     
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