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Using a Jeep to Estimate the Energy in GasolineProblem: Solution:
(10
mph)/(11 sec) = 0.91 mph/sec = 0.40 m/sec^{2}
and the force slowing the Jeep: (1400
kg) x (0.40 m/sec^{2})
560 nt
This force is the same force that must be overcome when driving the Jeep at constant speed. Since 20 miles/gal = 32,000 m/gal, the energy in j, expended by burning a gallon of gasoline to overcome 560 nt of force over the distance of one mile, is (560
nt) x (32,000 m/gal)
2 x 10^{7} j/gal.
Since engine efficiency is 20%, the actual energy expended must be about 5 times the above stated amount, or 10^{8}
j/gal,
the difference showing up as waste heat. Thus, burning a gallon of gasoline releases about 10^{8} j of energy. Exploding a ton of TNT liberates about 4 x 10^{9} j, so that a gallon of gasoline is equivalent to about 50 pounds of TNT. |
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