In: Physics

# 1. Real heat engines, like the gasoline engine in a car, always have some friction between...

1. Real heat engines, like the gasoline engine in a car, always have some friction

between their moving parts, although lubricants keep the friction to a minimum. Would a

heat engine with completely frictionless parts be 100% efficient? Why or why not? Does the

answer depend on whether or not the engine runs on the Carnot cycle? Again, why or why

not?

2.Some critics of biological evolution claim that it violates the second law of thermo-

dynamics, since evolution involves simple life forms developing into more complex and more

highly ordered organisms. Explain why this is not a valid arguement against evolution.

## Solutions

##### Expert Solution

1)

• Heat engines transfer energy from a hot reservoir to a colder reservoir and during this process it converts some energy to mechanical work.
• Carnot's theorem states that all heat engines between two heat reservoirs are less efficient than a Carnot heat engine operating between the same reservoir.
• Efficiency is given by

where,

Temperature of the cold reservoir

Temperature of the hot reservoir

• As you can see if 0 then efficiency is maximum.
• Real gas engines like gasoline engine in a car, due to friction, lose efficiency.
• Heat engine with completely frictionless parts be 100% efficient, the cold reservoir should be at absolute zero temperature.
• Yes the answer depend on whether or not the engine runs on the Carnot cycle because according to carnot theorem the carnot engine is the most efficient engine.

2)

• The second law of thermodynamics says that disorder, or entropy, always increases or stays the same over time, for an isolated system.
• But it is only valid in closed systems with no external source of energy.
• The earth as a system is not closed since it receives energy continuously from the sun. So the second law of thermodynamics cannot be applied.
• The universe on the other hand can be considered as an isolated system hence its total entropy is increasing. The same cannot be said for earth.

## Related Solutions

##### A gasoline engine is modified to run on hydrogen. Assuming hydrogen releases heat at the rate...
A gasoline engine is modified to run on hydrogen. Assuming hydrogen releases heat at the rate of 120 MJ/Kg when burnt, a. Write the chemical reaction involved in burning of hydrogen in air. b. Determine ratio of mass of air to fuel (A/F ratio) c. What is the fuel consumption rate, if engine produces 100 kW? The engine operates between combustion temperature of 585ºC and exhaust temperature of 50º C? d. What is the mass flow rate of water in...
##### does a heat engine reject some heat to a lower temperature resorvoir
does a heat engine reject some heat to a lower temperature resorvoir
##### Using the thermodynamic cycles, explain the difference between the heat engine (Carnot cycle) and Otto and Diesel engines. Why do Diesel engines require different types of fuel than the regular Otto Engine?
Problem 5 CH5/5ptsUsing the thermodynamic cycles, explain the difference between the heat engine (Carnot cycle) and Otto and Diesel engines. Why do Diesel engines require different types of fuel than the regular Otto Engine?
##### A mechanic is trying to tune the engines in a twin engine plane much like a...
A mechanic is trying to tune the engines in a twin engine plane much like a string instrument can be tuned by listening to the beat frequency when two notes are played simultaneously. The mechanic has one engine running perfectly at a desired 4500 rpm and is trying to adjust the other to the same speed. He slowly detunes the second engine from a larger rpm until he first discerns a beat frequency amplitude that occurs once every 12 s....
##### How high a hill can a car coast up (engine disengaged) if work done by friction...
How high a hill can a car coast up (engine disengaged) if work done by friction is negligible and its initial speed is 104 km/h? 42.6 m If, in actuality, a 870–kg car with an initial speed of 104 km/h is observed to coast up a hill to a height 31.9 m above its starting point, how much thermal energy was generated by friction? 9.11×104 J What is the average force of friction if the hill has a slope 7.7°...
##### 1. A nuclear power plant contains a heat engine that operates between the temperatures of 150oC...
1. A nuclear power plant contains a heat engine that operates between the temperatures of 150oC and 677oC. (a) What is the Carnot efficiency of the engine? (b) If the engine exhausts energy to the cold reservoir at a rate of QC = 7.0 × 108 J per second, how much heat energy must be flowing into the engine from the hot reservoir (QH) each second? 2. A house has a flat (horizontal) roof. If the wind then blows over...
##### A particular car engine operates between temperatures of 400°C (inside the cylinders of the engine) and...
A particular car engine operates between temperatures of 400°C (inside the cylinders of the engine) and 20°C (the temperature of the surroundings). Given these two temperatures, what is the maximum possible efficiency the car can have? (Note that actual car engine efficiencies are in the 20-25% range.) _______ % Part (b) A particular car engine operates between temperatures of 400°C (inside the cylinders of the engine) and 20°C (the temperature of the surroundings). If the car was somehow able to...
##### When a car corners at speed one is relying on the friction between the tyres and...
When a car corners at speed one is relying on the friction between the tyres and the road to counter the centrifugal force tending to throw the car outwards. One way to reduce the dependence on friction is to ‘bank’ the corner. For a car travelling with a speed v entering a corner of radius r, show that the angle of the bank, θ, (measured from the horizontal) should satisfy tanθ = v2/(gr) if there is to be no reliance...
##### 1: A car, A, is stationary with the engine running. A second car, car B, passes...
1: A car, A, is stationary with the engine running. A second car, car B, passes car A at a constant speed of 12 m/s. at this moment car A accelerates at 0.5 m/s2. A: Sketch the two events on the time vs position graph. B: How far down the road does car A catch car B.
##### Manufacturers of aircraft engines have, like many other industrial manufacturers, tried to make engines that are...
Manufacturers of aircraft engines have, like many other industrial manufacturers, tried to make engines that are more economical to operate while still providing the power needed to fly large-capacity aircraft. The Boeing 747, long considered the workhorse of the jumbo jet fleet, is powered by four engines, each capable of 44,700 lbs of thrust. Because 747’s have been around since 1969, maintenance costs now are relatively fixed; the goal for any airline is to plan for consistent, predictable maintenance costs....