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Question-A physicist, upon awaking one morning to find his stove out of order, decides to boil the water for his wife's coffee by shaking it in a thermos flask. Suppose that he uses 420 cm^3 of tap water at 55 degF, that the water falls 1.45 ft each shake, and that the physicist completes 26 shakes each minute. Neglecting any loss of thermal energy by the flask, how long must he shake the flask before the water boils?

Work-Alright, so we know that Q=m*c*(Tf-Ti). We know the density of the water and can easily obtain the mass from there (420 g). Cwater is equal to 4.186 J/(g*K). We can convert Fahrenheit to Kelvin (55 degF is 285.77777 degK). This is Ti and Tf is 373 K.

Q=420(4.186)(373-285.777)

Q=153383.764517

Now, calculate the work done by the shaken thermos. F*d (m*a*d). The mass is 420, the acceleration is (1.45 ft*26)/min*1/60 or .6283333. Set this equal to heat, with distance as a variable.

420*.6288*x=153383.764

x=580.7066 ft

Multiply by number of ft/s...

=364.87733 s

Does anyone know where I'm going wrong? Thank you so much in advance for any help you may give me.

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# Homework Help: Change in Temperature and Thermal Energy?

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