Question

15 In which of the following phenomena is surface tension important?
the floating of a boat in water
the floating of a steel wire in water
the floating of a ballon in air
the floating of a plastic sphere in water

16 Which of the following substances has the highest viscosity at room temperature?
Water
kerosine
palm oil
alcohol

17 An engine absorbs 2000J of heat from a hot reservoir and expels 750J to a cold reservoir during each operating cycle. What is the efficiency of the engine?
50%
62.5%
74.2%
85.6%

Answer 1

Question #58119, Physics / Molecular Physics | Thermodynamics |

15 In which of the following phenomena is surface tension important?

the floating of a boat in water

the floating of a steel wire in water

the floating of a ballon in air

the floating of a plastic sphere in water

16 Which of the following substances has the highest viscosity at room temperature?

Water

kerosine

palm oil

alcohol

17 An engine absorbs 2000J of heat from a hot reservoir and expels 750J to a cold reservoir during each operating cycle. What is the efficiency of the engine?

50%

62.5%

74.2%

85.6%

Answer:

15. ...the floating of a steel wire in water.

16. Dynamic viscosities of given substances at 300 K are:

Water 0.89×10⁻³ Pa·s

Alcohol (ethanol) 1.1×10⁻³ Pa·s

Palm oil 77.19×10⁻³ Pa·s

Kerosine 1.64×10⁻³ Pa·s

Hence, palm oil has the highest viscosity.

17. The efficiency of engine is defined:

η = (1 - Q1/Q2)×100%, where Q1 – the final heat and Q2 – the initial heat.

η = (1 - 750 J/2000 J)×100% = 62.50 %

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