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Physics & Collisions. Car, velocity, acceleration question.

  1. Apr 5, 2009 #1
    1. The problem statement, all variables and given/known data

    The red chief jumps into his heavy (20kg) jeep and presses the gas pedal. Instantly the engine revs and the vehicle begins to pull away. The chief has an interesting habit. He monitors the gauges in his vehicle in intervals of exactly 10 seconds and always drives straight since his steering wheel is broken. The first time he looks at his gauge it says that he is accelerating at 2 m/s/s. The second time he monitors his gauge he notes that the vehicle is now accelerating at 5 m/s/s, after a few minutes he decelerates and coasts along at a constant speed of 20m/s. He is now 1500km from his initial position. An instant later he notices that he had fallen off of a cliff, obviously affected by gravity (g = -9.81m/s/s). Maybe he shouldn’t keep checking his gauges and pay more attention to the road.

    Jeep: 20kg.
    Full distance: 1500km
    At 10s, Accel = 2m/s/s
    At 20s, Accel = 5m/s/s
    At 1500km before he falls off the cliff, he is going at a constant rate of 20m/s
    Gravity: -9.8m/s/s

    2. Relevant equations

    a = delta v / delta t
    x = x(initial) + v(initial)t + 1/2 at^2
    v = v(initial) + at

    3. The attempt at a solution

    (a) [1 mark] What is the vehicle’s initial position and velocity?

    Initial Velocity (0, 0) m/s
    Initial Position (0, 0) m/s

    (b) [1 mark] What is the vehicle’s velocity at time 1 second?

    We can't even get this far as we can't find out how to get v2 in this equation.

    a = v2-v1
    _____
    t2 - t1

    How can we get v2, if we have the time, but we don't have the acceleration at the single point. (1s)

    Please see if you can help us get v2. Thanks so much.
     
  2. jcsd
  3. Apr 6, 2009 #2
    NVM, i think we got it.
     
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