Answer
given,
Q₁ = 10,000 J
W = 2000 J
heat of combustion, Lc = 5 x 10⁴ J/g
W = Q₁ - Q₂
Q₂ = Q₁ - W
Q₂ = 10,000 - 2000
Q₂ = 8000 J
Q₂ is the rejected to heat.
a) thermal efficiency of this engine
[tex]\eta = \dfrac{W}{Q_1}\times 100[/tex]
[tex]\eta = \dfrac{2000}{10000}\times 100[/tex]
[tex]\eta =20 \%[/tex]
b) discarded heat is equal to 8000 J.
c) Power output
P = N W
N = 25 cycle/s
P = 25 x 2000 = 50000 W
1 W = 746 Horsepower
Power in horsepower
[tex]P = \dfrac{50000}{746}[/tex]
P = 67 HP
d) gasoline burnt is equal to
Q₁ = m Lc
[tex]m = \dfrac{Q_1}{L_c}[/tex]
[tex]m = \dfrac{10000}{5\times 10^4}[/tex]
m = 0.2 gram/cycle
e) gasoline burnt per hour
[tex]\dot{M} = N.m[/tex]
[tex]\dot{M} = 25\times 0.2[/tex]
[tex]\dot{M} =5 gm/s[/tex]
1 Hr = 3600 s
[tex]\dot{M} =5 \times 3600[/tex]
[tex]\dot{M} =18000\ g/hr[/tex]
