Confusing chemical energy reaction question:)?

Question

A particular car travels 20000km in a year and operates at a 20% effiency in transforming the chemical energy in fuel into mechanical energy(motion). The car has a fuel consumption of 10L per 100km and its petrol tank holds 50L

a. The amount of energy supplied by a full tank of petrol

b. the amount of energy released as watse heat during the year

Answer 1

http://bioenergy.ornl.gov/papers/misc/en...

Gasoline: US gallon = 115,000 Btu = 121 MJ = 32 MJ/liter (LHV). HHV = 125,000 Btu/gallon = 132 MJ/gallon = 35 MJ/liter

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1 tank @ 50 litres / tank = 50 litres

50 litres @ 35 MJ/liter = 1750 Mega Joules

1750 Mega Joules @ 20% = 350 MegaJoules are effective

your answers:

1750megaJoules are available in 50 Litres of petrol

350 MJ can be converted into motion from the 50 litres

1400 Mj will be wasted

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b. the amount of energy released as watse heat during the year

20,000 km @ 10 L  / 100 km = 2,000 litres

2,000 litres @ 1,400MJ wasted / 50 litres =

your answer is: 56,000 megaJoules will be wasted / year

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p.s.  

http://www.onlineconversion.com/energy.h...

56,000 megaJoules = 53, 000,000 Btu