April 20, 2014

Homework Help: Science - BTUs Please help

Posted by Sejul on Monday, September 3, 2012 at 12:33pm.

Although I vaguely see DrBob222's concept, I still need some help in the set up. Thank you.

A 10 lb. frozen boneless roast needs to be thawed and baked to a temperature of 200 degrees F.
The storage freezer maintains a temperature of -10 degrees F.
Pork changes from solid to a thawed state at 30 degrees F and has the following properties:
Heat Capacity "c" (frozen) = 0.50 BTU/(lb x F degrees)
"c" thawed = 1.2 BTU/(lb. x F degrees)
Heat of fusion (hf) = 125 BTU/lb.

How many BTUs does it take to bring the roast to a tasty 200 degrees F?

•Science - DrBob222, Sunday, September 2, 2012 at 6:47pm

q1 is heat from -10 to 30
q1 = mass x specific heat of frozen x (Tfinal-Tinitial)

q2 = heat at 30 to thaw at 30.
q2 = mass x heat fusion

q3 = heat from 30 to 200
q3 = mass x specific heat of thawed x (Tfinal-Tinitial)

Total heat = q1 + q2 + q3

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