Thermodynamics worksheet (continued) 1) How long does a 65 kg person have to wor

Question

Thermodynamics worksheet (continued) 1) How long does a 65 kg person have to workout on a stairmaster to "burn" off a 350 Calorie twinkie (humans are 30% efficient food engines). 1 "step-33m; 2 steps/sec [18 min1 n cooling: How many Watts of waste heat do you need to transfer (conduction and 2a) Huma radiation) in order to keep temperature stable while "burning off" the twinkie? (1000 W!!) And: 2b) HW 19-60 /1mm] 3) Coal plant: HW 20-65 (demo in class) 4) Cars: A typical compact car experiences drag of about 350N at 55 mph. If it gets 32 mpg at this speed, what is its efficiency? 1 gal of gas . 3.8 L Een-3.2 x 10,/L [15%) 5) Use the answer from HW 19-71 to estimate how much heat power is carried by the Guf Stream if it is 100 km wide, I km deep, and has a temp delta of 10° C while moving at 2.5 m/s.

Explanation / Answer

1)

m = mass of the person = 65 kg

t = time taken

n = number of steps = 2 t

h = height = 0.33 n = 0.33 x 2 x t = 0.66 t

E = energy = 0.30 x 350 = 105 cal = 439320 J

energy is given as

E = mg h

439320 = (65 x 9.8 x 0.66) t

t = 1045 sec = 18 min

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