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Answers will only be rewarded, if steps are shown to get to the answer. *please explain as if it were to a beginner* Thank you.

13) In figure 14.3, heat is added to a pure substance in a closed container at a constant rate. A graph of the temperature of the substance as a function of time is shown here. If LF= latent heat of fusion and LV= latent heat of vaporization, what is the value of the ratio LV/LF for this substance?

A) 4.5

B) 5.0

C) 7.2

D) 3.5

E) 1.5

14) A reversible engine operating between 500 K and 300 K has the same efficiency as a reversible engine operating between 400 K and what lower temperature?

A) 280K

B) 200K

C) 220K

D) 240K

E) 260K

15) A monatomic ideal gas with an initial pressure of 500 kPa and an initial volume of 1.80L expands isothermally to a final volume of 5.20 L. How much work is done on the gas in this process?

A) 900 J

B) 1570 J

C) 1700 J

D) 955 J

E) 875 J

16) A 3.1 kg solid sphere, made of metal whose density is 4900 kg/m ^3, is suspended by a cord. The density of water is 1000 kg/ m^3. When the sphere is immersed in water, the tension in the cord is closest to:

A) 37 N

B) 33 N

C) 24 N

D) 30 N

E) 27 N

Explanation / Answer

13)latent heat is diretctly proportional to heat provided

LF is at small horizontal line and LV is at large horizontal line in the graph

So LV/LF =7/2=3.5 (ratio of length of those horizontal lines)

14)efficiency=1-lower temperature/higher temperature

So 1-300/500=1-x/400 =>x=1200/5=240K

15)Work done in isothermal process =nRT ln(final volume/initial volume)

Also PV=nRT

So work=P(initial)*V(initial)*ln(V(final/V(initial))=500*1.8*ln(5.2/1.8)=955 J

16)buoyancy force acts upwards,Gravity acts down wards and rension acts upwards.So Using free body diagram,at equilibrium

Net upward force=net downwars force

Buoyancy force=density of metal*acceleration due to gravity*diameter of sphere

volume=mass/density=3.1/4900=0.63*10^-3 m^3

4/3*pi*(d/2)^3=0.63*10^-3=>d=0.63*10^-3*3/(4*3.14)=0.053m

diameter of sphere=0.053m

Tension=3.1*9.8-4.9*9.8*0.053=27N

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