Term
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The depth of some water is 65m. The density of the water is 1000kg/m3. The gravitational field strength g is 10N/kg. What is the pressure exerted at the base of the dam?
A. 15.4 Pa B. 154 Pa C. 165000 Pa D. 650000 Pa |
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Definition
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Answer: D. 650000 Pa
Method:
p = Pgh
pressure = density x gravity x height
pressure = 1000 x 65 x 10
= 650000 Pa |
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Term
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A gas is trapped inside a cylinder by a piston. The initial pressure of the gas is 500kPa when the volume of gas is 150cm3. The piston is now pushed in to compress the gas to a volume of 120cm3. Assuming there is no change on the temperature of the gas, calculate the new pressure exerted by the gas. |
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Definition
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Method:
p1V1 = p2V2
500,000 x 150 = p2 x 120
p2 = (500,000 x 150) / 120
p2 = 625kPa
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Term
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When a liquid evaporates, some of its molecules escape from the surface and the temperature of the liquid changes. Which row describes the escaping molecules and the change in temperature of the liquid?
escaping molecules temperature of the liquid
A. less energetic goes down
B. less energetic goes up
C. more energetic goes down
D. more energetic goes up |
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Definition
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Answer: C. More energetic escaping molecules, temperature of the liquid goes down.
Evaporation occurs when fast moving molecules escape the intermolecular forces of the liquid and become a gas. The temperature of a liquid determines the average kinetic energy of its molecules. When the higher energy molecules escape, this causes the average kinetic energy, and therefore the temperature, of the liquid to decrease. |
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Term
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Why does the temperature of water remain constant during melting and boiling? |
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Definition
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Answer: Because when a solid/liquid is heated, its molecules move faster and gain Kinetic Energy until some of them break lose and escape the solid/liquid. As the most energetic molecules have escaped, the temperature of the substance actually remains constant. As more heat energy is added, more molecules continue to escape the solid/liquid. Finally, when all have escaped and formed a liquid/gas, the temperature can begin to rise.
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Term
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How much energy is needed to change the state of 750g of ice at 0 degrees Celsius to water at 0 degrees Celsius?
SLH of fusion = 340J/g. |
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Definition
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Answer: 255kJ
Method:
L = Q/m
Q = mL
Q = 750 x 340
= 255,000J
= 255kJ |
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