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Homework Help: Problem about a car

  1. Nov 30, 2006 #1
    This problem is in various questions, so please bear with me.

    1. The problem statement, all variables and given/known data
    a) A car weighing 1000 kg is accelerated at 3 m/sec^2. What is the force required to produce that acceleration?.

    b) in problem a- the car is accelerated for 45 seconds. How fast in m/sec is it going at the end of 45 sec?

    c) in problem b- after the initial 45 second acceleration period, the car coasts (no net forces) for 20 minutes. ca) How fast is it going at the end of 20 minutes? How far did it go in hat 20 mintues?
    cb) How much work was done on the car in that 20 minutes?
    cc)At the end of the 20 minute coast period, the car is decelerated to a stop. How much work was done to bring the car to a stop?
    cd)If the car took 35 seconds to stop, what was the force on the car and how far did it travel in the meters before it stopped

    2. Relevant equations
    a) F=ma
    b) Vf(final velocity)= Vo(initial velocity) + a(acceleration)T(time)
    c) F=ma or Vf=Vo+aT or S(distance)=VoT+ 1/2(a)(T^2) or W(work)=(F)D
    (D is distance)
    3. The attempt at a solution
    a) F=ma
    F=1000kg(3 m/sec^2)
    F=3000 N

    b) Vf=Vo+aT
    Vf=0+3 m/sec^2(45 sec)
    Vf=135 m/sec

  2. jcsd
  3. Nov 30, 2006 #2


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    Staff: Mentor

    ca) coasting means what about its speed? If you know how fast it was going for the 20 minutes....how far did it cover?

    cb) What is the definition of work? Can you do work if F=0?

    cc) What can you say about the kinetic energy of the car as it goes from 135m/s to 0m/s? Where did that energy go?

    cd) Re-use the technique you used in 3a.
  4. Nov 30, 2006 #3
    ca) coasting means that the speed stayed the same throughout the 20 minutes?

    cb) Work is the exertion or effort directed to produce or accomplish something. I guess that one can not do work if there is no force. I still don't postulate how this answers the question.

    cc) The kinetic energy stops being present? The energy just dissipated.

    cd) Reusing the formula F=ma would mean that I would have to multiply 1000kg by the acceleration of the car which I really do not know what it is.

    I am very perplexed!@!#!
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