2.1.2. Particle model
A subsection of Physics, 5054, through 2. Thermal physics
Listing 10 of 76 questions
shows a cylinder with a piston that contains a gas. gas cylinder piston A liquid occupies a much smaller volume than a gas which has the same number of molecules. Explain why there is this difference. The volume of the gas changes from V1 to V2 as the piston moves into the cylinder. This increases the pressure from p1 to p2. The temperature remains the same. State the formula that relates V1, V2, p1 and p2. The initial pressure of the gas in the cylinder is 1.2 × 105 Pa and its initial volume is 100 cm3. The cross-sectional area of the piston is 5.0 cm2. The piston is pushed in a distance of 8.0 cm. Calculate the final pressure of the gas in the cylinder. pressure = Explain, using ideas about molecules, why the pressure of the gas changes.
5054_s19_qp_21
THEORY
2019
Paper 2, Variant 1
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A fixed mass of gas in a glass tube is trapped by a seal at one end of the tube and by a column of mercury. The mercury is free to move within the tube. The tube is rotated slowly from the vertical as shown in to the horizontal as shown in . The volume of the gas increases and its temperature remains constant. mercury mercury gas gas 0.30 m sealed end sealed end (not to scale) Describe why rotating the tube changes the pressure of the gas in the sealed end. Explain, using ideas about particles, why the pressure of the gas decreases when its volume increases. In the length of the mercury column is 0.30 m. The density of mercury is 14 000 kg / m3. Atmospheric pressure is 1.0 × 105 Pa. Calculate the pressure of the gas in the tube. pressure = Pa (not to scale) The pressure of a different sample of gas changes at constant temperature. shows one point, marked X, on a graph of pressure against volume for the gas sample. At X the pressure of the gas is P0 and its volume is V0. 2P0 P0 ½P0 ½V0 V0 2V0 volume pressure X On , sketch the graph as the pressure of the gas decreases from 2P0 to ½P0.
5054_s23_qp_22
THEORY
2023
Paper 2, Variant 2
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Many cars are fitted with an air-bag, as shown in . In a collision, the air-bag inflates and reduces the effect of the impact between the passenger and the dashboard. air-bag dashboard In a test of the air-bag, a heavy ball is used instead of the passenger. The car is travelling at 14 m / s when it hits a wall. The air-bag inflates and the ball takes 3.0 s to come to rest. The ball has mass 5.0 kg. Calculate the average deceleration of the ball. Calculate the average force exerted on the ball. Using ideas about acceleration, explain how the air-bag reduces the force on the ball during the test. If there was no air-bag, a large pressure would be exerted on the ball at the point where it hits the dashboard. Define pressure. The inflated air-bag reduces the pressure exerted on the ball. State two reasons why the pressure is reduced. Compressed gas from a small cylinder inflates the air-bag. The cylinder contains a volume of 600 cm3 of gas at a pressure of 1.4 × 107 Pa. The cylinder and the inflated air- bag have a volume of 30 000 cm3. Calculate the pressure of the gas in the inflated air-bag, assuming that the temperature is constant. The pressure inside the cylinder decreases as the air-bag is inflated. Explain, using ideas about molecules, why the pressure decreases.
5054_w07_qp_2
THEORY
2007
Paper 2, Variant 0
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A car has a gas-filled shock absorber for each of its four wheels. shows one of these shock absorbers. attached to car body trapped gas piston cylinder axle The axles are attached to the cylinders. The body of the car is supported by the four pistons, which can move up and down inside the cylinders. Each piston has a cross-sectional area of 35 cm2. A driver of mass 70 kg gets into the car. Calculate the driver’s weight, weight = the average increase in the pressure of the gas in the cylinders. pressure increase = Explain in detail how the molecules of the gas trapped inside the cylinder by the piston exert a pressure on the cylinder. The temperature of the trapped gas remains constant. Explain why the pressure of the gas increases as the piston is moved further into the cylinder. At the end of a long journey, the temperature of the trapped gas in the shock absorbers has increased substantially. State what happens to the molecules of the trapped gas due to the temperature increase. State and explain the effect of the increased temperature of the gas on the height of the car body above the road surface.
5054_w10_qp_21
THEORY
2010
Paper 2, Variant 1
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A schoolboy tries to inflate a bicycle tyre using a bicycle pump. Explain how the air molecules inside the pump produce a pressure. The opening at the end of the pump is blocked with a small amount of dried earth, as shown in . pump dried earth air The air is initially at a pressure of 100 kPa. During one stroke of the pump, the volume of air in the pump is reduced from 120 cm3 to 16 cm3. Assuming that the temperature of the air remains constant, calculate the pressure of the compressed air. pressure = Compressed air in the pump at this pressure exerts a force on the dried earth. The cross-sectional area of the opening at the end of the pump is 1.2 × 10–5 m2. Calculate the size of this force. force = In fact, the temperature of the air in the pump increases as its volume decreases. The actual pressure of the 16 cm3 of air differs from the pressure calculated in . Using ideas about molecules, state and explain this difference.
5054_w13_qp_21
THEORY
2013
Paper 2, Variant 1
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A gas is trapped at atmospheric pressure in a cylinder by a piston. The piston is held in a fixed position by a movable rod. shows the cylinder. piston rod cylinder trapped gas The cylinder is heated. As the temperature of the gas increases, its pressure increases. Explain, in terms of molecules, why the pressure of the trapped gas increases. The rod is pulled down and the piston is then free to move as shown in . trapped gas piston cylinder rod As the piston moves, the temperature of the gas remains constant. State and explain, in terms of molecules, what happens to the pressure of the gas.
5054_w15_qp_22
THEORY
2015
Paper 2, Variant 2
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Gas is trapped in a syringe by a piston. shows that the narrow end of the syringe is sealed. syringe sealed end gas piston When the gas is at a pressure of 1.1 × 105 Pa, it occupies a volume of 40 cm3. Explain, in terms of the molecules, how the gas exerts a pressure on the inside of the syringe. The piston is slowly pulled to the right until the volume occupied by the gas is 110 cm3. The temperature of the gas does not change. Calculate the new pressure of the gas. pressure =
5054_w16_qp_22
THEORY
2016
Paper 2, Variant 2
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Questions Discovered
76