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1. convert the following temps Please show work for this too

a)90 deg F to ____deg C

b) -29 deg C to ____ deg F

c) -94 deg F to ______K

d) 98.6 deg F to ______deg C

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2. Highway slabs of concrete are poured in lengths of 10.0 m.

How wide should the expansion gaps between the slabe be at a

temperature of 20.0 deg C to make sure that there will be no

contact between adjacent slabs over a temperature rang of -25 deg C

to 45 deg C

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3.Calculate the total quantity of heat in both "J-joules" and

"Kcal-Kilocalories" required to change 1.00 kg of ice at -20.0 deg

C to steam at 120.0 deg C. note that this process requires a total

of several calculations that include phase changes. Assume that

there are no losses of mass or temperature in the conversions.

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4. a heat engine absorbs 250 Kcal of heat from a high

temperature reservoir and exhausts 175 Kcal to a low temperature

reservoir.

a) determine the engines thermal efficiency from the efficiency

of an idea gas heat engine.

b) from the efficiency that you have calcualted , how much heat

is actually converted into useful work?

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Explanation / Answer

1.

32.22

-20.2

-70

-72.5

2.

At 45 °C, the slab expands for ΔL = L α ΔT =10.0 m x 1.2 x 10^-5 /K x 25 K = 0.00300 m =3.0 mm.

This is also the minimum crack between the slabs (at lower temperatures, the slab contracts).

4.

The efficiency of a heat engine is given by

n = Wu / QH

Where

Wu - is the useful work (250Kcal)

QH - Heat taken from the hot reservoir (175 Kcal)

So n = 175 / 250) =0.7

and since you want that in percent multiply the result by 100.

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