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Question about power and output power.

  1. Jun 11, 2014 #1
    1. How could you measure your output power developed while pushing a car?


    2. If you developed a certain amount of power running up lets say 2 flights of stairs, could you develop the same power if you ran up twice as many stairs?


    3. What factors affect a persons output power running up stairs?
     
  2. jcsd
  3. Jun 11, 2014 #2
    You need to try to solve the problem before we can help you. Show us your progress.
     
  4. Jun 12, 2014 #3
    1.
    Rough guess :
    Level road assumed, tyres at recommended pressure.

    m = mass of the car in kg
    g = local gravity rate ( use 9.81 (m/s)/s )
    Crr = tyre on ashphalt rolling resistance co-efficient ( use 0.03 )

    Rolling resistance force (f) ( constant, regardless of speed ) = m * g * Crr
    ( answer is in Newtons )

    Find the maximum speed (v) you can push the car in metres per second
    (mph * 0.44704 = metres per second)

    Then :
    The power provided (W) to push the car :
    W = f * v
    (answer is in Watts, divide by 745.7 to get horsepower)

    Example :
    v = maximum push speed = 4 m/s (example)
    m = 1,500 kg
    g = 9.81 (m/s)/s
    Crr = 0.03

    f = m * g * Crr
    f = 1,500 * 9.81 * 0.03
    f = 441.45 Newtons

    W = f * v
    W = 441.45 * 4
    W = 1,765.8 Watts ( about 2.37 hp )

    2.
    Energy change (Joules) = m * g * h
    m = your mass in kg
    g = local gravity rate (use 9.81 (m/s)/s)
    h = vertical height moved in metres (floor to floor difference)
    Then :
    Average Power = energy change / time in seconds
    3.
    Power output is roughly proportional to your size, but includes factors like sex, fitness level, nutrition etc.
     
  5. Jun 12, 2014 #4

    BvU

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Hello vegie, and welcome to PF.

    You show us the questions that were put to you. Which question are you putting to PF ?

    Anyway, for # 1 I would use a scale between my hands and the car to have guess for the force. Push a certain distance in a certain time and there you are !

    (How many tyres does Dean's car have? And does he really think he can push hard enough to get a meaningful furlongs/fortnight -- oh, sorry, mph -- reading from the speedometer ?)

    Share your work, Veggie !
     
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