I don\'t get how to do this problem. Do I use Q =mcT? A car engine wastes 90% of

Question

I don't get how to do this problem. Do I use Q =mcT? A car engine wastes 90% of its energy as heat. If thecar burns a gallon of gas (3785g), a) How much heat (in calories) does it "dump" into theair? b) How much work can it do (in Joules)? -On part b), do I convert the calories to joules? According to my teacher, the answer for a) is 3.4 x 107 calories b) is 1.59 x 107 J I don't get how to do this problem. Do I use Q =mcT? A car engine wastes 90% of its energy as heat. If thecar burns a gallon of gas (3785g), a) How much heat (in calories) does it "dump" into theair? b) How much work can it do (in Joules)? -On part b), do I convert the calories to joules? According to my teacher, the answer for a) is 3.4 x 107 calories b) is 1.59 x 107 J

Explanation / Answer

   Calorific value ofgas   =   46.4 *103   J/g    Energy released pergallon   E   =  46.4 *103 * 3785   =   1.76 *108   J    a.   Energy dumped inatmosphere   Eair   =   90%of E   =   0.9 * 1.76 *108   =   1.60 *108   J          Incalorie         Eair   =   1.60* 108 / 4.18   =   3.83 *107   cal.      (4.18 J = 1 Cal.)    b.   Energy converted towork   Ework   =   10%* E   =   1.76 * 108 *0.1   =   1.76 *107   J

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