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Conservation of Energy, Car Driving with Drag Force

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  1. Nov 9, 2014 #1
    1. The problem statement, all variables and given/known data
    A 710kg car drives at a constant speed of 23m/s . It is subject to a drag force of 500 N. What power is required from the car's engine to drive the car (a) on level ground? (b) up a hill with a slope of 2.0o? Express your answer to two significant figures.

    2. Relevant equations
    p = mv
    P = ΔW/Δt (but no time information given)

    3. The attempt at a solution
    I am not sure where to begin. I understand that power is the change in work with respect to time, but there is no time information given in the problem, so I am a little lost.
     
  2. jcsd
  3. Nov 9, 2014 #2

    SteamKing

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    The car is moving on level ground and up the hill at constant speed. Speed has got time in it. Why can't you use that?
     
  4. Dec 20, 2014 #3
    Since constant speed is the situation, the for and against forces are equal.
    On level ground the mass of the car doesnt come into it.
    Then :
    Power consumption ( Watts ) = force overcome (N) * speed (m/s)
    (applies to constant or instantaneous speed only)
    In the uphill problem, calculate the additional force acting against the car and down the slope due to gravity ( m * g * sine (2 ° ) ) and add to the 500 Newtons of drag, then calculate the power consumption.
     
  5. Dec 20, 2014 #4

    SteamKing

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    This question is probably moot by now, given that it was first posted in Nov. 2014 and the OP never replied.
     
  6. Dec 20, 2014 #5
    OK, thanks
     
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