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I've figured out part of the problem but cannot figure out the rest HELPPPPPPP PLEASE

  1. Oct 6, 2008 #1
    PLEASE HELP I'M CLUELESS ON THESE PROBLEMS

    FOR THIS QUESTION I FOUND B BUT I HAVE NO IDEA ON HOW TO FIND A.

    A plane weighing 220 kN (25 tons) lands on an aircraft carrier. The plane is moving horizontally at 62 m/s (139 mi/h) when its tailhook grabs hold of the arresting cables. The cables bring the plane to a stop in a distance of 88 m.
    (a) How much work is done on the plane by the arresting cables?
    MJ

    (b) What is the force (assumed constant) exerted on the plane by the cables?
    kN opposite the plane's direction of motion
    (Note: Both answers will be underestimates, since the plane lands with the engines full throttle forward; in case the tailhook fails to grab hold of the cables, the pilot must be ready for immediate takeoff.)

    AND FOR THIS QUESTION I FOUND A BUT HAVE NO IDEA ON HOW TO FIND B.


    A car with mass of 1000.0 kg accelerates from 0 m/s to 40.0 m/s in 12.0 s. Ignore air resistance. The engine has a 23% efficiency, which means that 23% of the thermal energy released by the burning gasoline is converted into mechanical energy.
    (a) What is the average mechanical power output of the engine?
    kW
    (b) What volume of gasoline is consumed? Assume that the burning of 1.0 L of gasoline releases 47 MJ of thermal energy.
    L
     
  2. jcsd
  3. Oct 6, 2008 #2

    Kurdt

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  4. Oct 6, 2008 #3

    HallsofIvy

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    Re: i've figured out part of the problem but cannot figure out the rest HELPPPPPPP PL

    You've already done (a)? That should have been easy: the airplanes kinetic energy is reduced to 0 by the work done. For (b), now use that: Work= Force times distance. You know the work done, divide by the distance it takes to stop the airplane.

    For the second problem, the car's kinetic energy has gone from 0 to (1/2) mv2. How much work must have been done? "Power" is work divided by time. That total energy is 23% of the actual energy produced by the gasoline and you are told that "burning of 1.0 L of gasoline releases 47 MJ of energy".
     
  5. Oct 6, 2008 #4
    Re: i've figured out part of the problem but cannot figure out the rest HELPPPPPPP PL

    OKAY SO FOR THE FIRST QUESTION
    WORK = KINETIC ENERGY

    SOOOO
    Average impact force x distance traveled = change in kinetic energy

    f=MA
    F=22448.9 KG* 490.3=11006695.67

    CHANGE IN KINETIC ENERGY= 11006695.67* 88= 968589218.96

    IS THIS RIGHT??
     
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