Friday, September 10, 2010

Kinetic energy of Flight 11

The kinetic energy (KE) of a moving object is given by the formula

E = 1/2 m * v2

Where, in the case of flight AA 11:

  • m is the mass of the plane: That is, empty mass plus fuel load plus passengers, their baggage, and additional cargo. AA 11 was a Boeing 767-223ER, which has an operating emtpy weight of 82,380kg and a maximum take-off weight of 179,170kg. Maxium fuel capacity is 90,770l (see Boeing technical specs). Maximum range is 12,195 km. Flight AA11 had 158 passenger seats, but only 81 passengers (51% capacity), plus 11 crew members. 92 passengers, weighing on average 70kg, have a mass of 6,440kg. For each, luggage, food, drinks and other supplies of 20kg may be added, or 1,840kg. It was scheduled to fly from Boston to Los Angeles, a distance of about 30% of its maximum range. Wikipedia, quoting NIST, states that it carried about 38,000l of fuel - about 42% of maximum fuel capacity, by the time of impact. Jet fuel has a specific weight of about 0.8 kg/l, so 38,000l fuel is about 30,000kg. The total mass of the plabe was thus at least:
    m = 82,380kg + (6,440+1,840)kg + 30,000kg = 120,660kg
    (empty weight + passengers + fuel)
  • v is the velocity of the plane at impact, which was estimated by NIST as 750km/h or 208m/s

Using these estimates, the kinetic energy of flight AA11 works out as

Ekin = 1/2 * 120,660kg * (208m/s)2 = 2.61 * 109J

There are, however, other numbers available for mass an velocity: NIST: 443mph = 198m/s, which would lower my estimate to 2.365 * 109J

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