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Physics, 22.05.2020 08:05 moonk7733

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2. You're sitting on a warm granite rock, enjoying the sunshine. You decide it's time to test the water. You take off your shoes and walk across the cool sand to the water. You wade into the water, enough to cover your feet. Brrr! The water is cold. You will have to wear a dry suit when you go diving. (16 points)
a. Which item - the granite rock, the sand, or the water - has the highest specific heat? Which has the lowest specific heat? (4 points)

b. Which item requires the least energy to increase its temperature? Explain your answer in terms of this item's specific heat. (4 points)

c. If the granite rock on which you were sitting has a specific heat of 600 J/(kg°C), how much energy must be added to a 2-kilogram piece of it to increase its temperature from 20°C to 30°C? Show your work, including the equation you need to perform this calculation. (4 points)

Q = 2 kg * 600 J/(kg*deg C) * (30 deg C - 20 deg C)
Q = 12000 J
You need to add 12 kJ.

d. What is the second law of thermodynamics? Use this law to describe why your feet got cold, not hot, when you put them in the water. (4 points)

The second law of thermodynamics describes the flow of heat. Heat flows from an object at higher temperature to the body at colder temperature. It does not flow in the opposite direction.

When you put your feet into the water. The heat from our feet will get transferred to the water. That's why feet gets cold but not get hot when you put them into the water.

3. Before you get ready to go diving, you want to explore the area. You see a small snowpack across a small bridge, a short walk away. As you approach the bridge, you notice interlocking metal joints that join the bridge to the road. What are these joints called? What purpose do they serve? Describe thermal expansion, and explain why these joints are necessary. (4 points)
Expansion joint:

An Expansion joint or also referred to as the movement joint, it is an assembly made to safely absorb the temperature-induced expansion between two structures and the contraction of the construction materials used for the structure. The joints also absorb vibrations, and to hold parts together even though stressors are present, stressors can be known characterized as the strong winds, seismic activities, and temperature changes in the area.

4. When you get to the snow, you grab a handful to take back to the beach. However, by the time you get there, the snow has disappeared, and you are left with water dripping down your arm. (10 points)
a. Describe the phase change that happened to the snow in your hands. What happened to the snow's molecules during this phase change? (3 points)

b. If the water continued to heat, what would be its next phase change? (3 points)

c. Did the snow's entropy increase or decrease while in your hand? Explain your answer. (4 points)

5. At last, it's time to go diving! You are going to dive offshore, but you'll need to drive to the site. You load your gear into the trunk of the car and take off. (10 points)
a. What type of device does the car use to move? Describe in terms of the second law of thermodynamics, and draw a diagram of how this device operates. (6 points)

The boat uses an engine which provides it the kinetic energy to move. The engine uses gasoline, or manual paddles, push pole or propeller.

b. If the car's engine has a heat input of 30,000 J, with 22,500 J going to outside surroundings, what is its efficiency? Show your work, including the equation you need to perform this calculation. (4 points)

efficiency= output/input= (30,000-22,500)/30,000=0.25
0.25*100%=25%

6. You get to your dive site and park the car. You put on your gear and get ready to enter the water. But first you check your scuba tank. It is filled to a pressure of about 25,000 kPa at 300 K. The volume of the tank is 25 L. You begin to wonder: If pressure remains constant, what would happen to the volume of gas in the tank if its temperature increased? (6 points)
a. Which of the four thermal processes describes the temperature-volume relationship at constant pressure? (3 points)

b. Write the equation for this process. Hint: Think about the first law of thermodynamics. (3 points)

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