SARC 122 Assignment 8

Question 1
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An ideal Carnot engine operates between 500°C and 100°C with a
thermal energy input of 2501 per cycle.
(a) Sketch an energy transfer diagram for this engine. __ _5r”‘?-‘3-‘1″-‘j”” Y. . ‘i
(b) What is the efficiency of this engine? _-.-‘-‘-‘-” ‘ ‘ 1*
(c) How much thermal energy is delivered to the cold reservoir ‘ ‘ .’ ‘N “fl” ‘ -‘ ‘3
in each cycle?
(d) What minimum number of cycles is needed for the engine to raise a 500 kg rock to a height of 10 m?
Question 2 heat pump
A heat pump transfers energy from cold outside air to
warmer air inside a house with a COP of 3.80 and a power
consumption of 7.03 kW °”t5’de ‘”5’de
(a) Sketch an energy transfer diagram for the heat Q“ Qh
pump. Tc Th
(b) Use it to determine how much energy is transferred E‘
into the house during 8.0 hours of continuous
(c) How much energy is transferred from the outside air?
Question 3
(a) The pressure exerted on the ground by an elephant’s weight spread evenly over its four feet is less
than atmospheric pressure. Why, then, would you be crushed under the foot of an elephant, while
you are unharmed by the pressure of the atmosphere?
(b) A building is supported on 40 piles each of base area 0.1 m2. .I
The soil below the piles can withstand a pressure of 200 kPa. B B
What is the maximum weight of the building? B E E
(c) Why are people confined to bed less likely to develop bedsores on their
bodies if they lie on a waterbed rather than an ordinary mattress? 1 i‘_
(d) You see here a water tank on top of a New York apartment building.
It is made of wood and reinforced with metal hoops.
Why is it on top of the building? I_
Why are the hoops closer together near the bottom of the tank?

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