1. 1
   A warehouse manager is deciding where a heavy safe can be placed on a wooden storage floor. The safe has a mass of 300 kg and rests on four rectangular feet, each with an area of 0.015 m2. (Use g = 10 N/kg.)

   (a)

   Which equation is used to calculate the pressure exerted by an object on a surface?

   [1 mark]

   • Ap = F / A
   • Bp = A / F
   • Cp = F x A
   • Dp = F + A

   (b)

   If the safe's feet were replaced with feet of smaller total area but the safe's weight stayed the same, what would happen to the pressure it exerts on the floor?

   [1 mark]

   • AIt would decrease
   • BIt would increase
   • CIt would stay the same
   • DIt would become zero

   (c)

   Calculate the pressure the safe exerts on the floor.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A campsite water heater uses a gas burner to heat a fixed mass of 1.5 kg of water in a metal kettle, starting at 20 degC, until it boils steadily at 100 degC. The specific heat capacity of water is 4200 J/(kg degC).

   (a)

   Once the water in the kettle has reached 100 degC and is boiling steadily, which quantity continues to increase as the burner keeps supplying energy to it?

   [1 mark]

   • AThe temperature of the liquid water
   • BThe kinetic energy of the individual water molecules remaining in the liquid
   • CThe internal energy stored by the water molecules as they escape into steam
   • DThe speed of the water molecules remaining in the kettle

   (b)

   Which statement correctly describes the arrangement and motion of the particles in the steam leaving the kettle, compared with the boiling water it came from?

   [1 mark]

   • AClose together in a fixed regular pattern
   • BClose together but free to move past each other
   • CIdentical arrangement to the liquid, just hotter
   • DFar apart and moving randomly at high speed

   (c)

   Calculate the energy required to raise the temperature of the 1.5 kg of water from 20 degC to its boiling point of 100 degC.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A hospital's spare oxygen cylinder is stored in a supply room. The cylinder has rigid walls, so the volume of the gas it contains cannot change. Initially, the oxygen inside is at a temperature of 27 degC and a pressure of 300 kPa. A fire in a neighbouring room causes the temperature in the supply room, and hence the temperature of the oxygen in the cylinder, to rise to 127 degC.

   (a)

   Explain, in terms of the motion of the oxygen molecules, why the pressure inside the cylinder increases as its temperature rises.

   [3 marks]

   (b)

   Calculate the pressure inside the cylinder once its temperature has risen to 127 degC.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   An Antarctic research team observes a large iceberg floating in the ocean, with most of its volume submerged below the surface. Ice is less dense than the surrounding sea water. Over several weeks of warmer air temperatures, part of the iceberg melts at its surface, turning to liquid water that drains away into the sea.

   (a)

   Explain, in terms of the arrangement and motion of the water particles, what happens as part of the solid ice melts into liquid water.

   [6 marks]

   (b)

   Explain, using ideas about density, why the iceberg floats with most of its volume below the surface, and explain how the pressure on its submerged surface varies with depth.

   [6 marks]

   Total for question 4: 12 marks

5. 5
   A quality-control technician at an olive oil bottling plant takes a sample of the oil for testing. The sample has a volume of 200 cm3 (0.0002 m3) and a mass of 184 g (0.184 kg).

   (a)

   Which equation is used to calculate the density of a substance from its mass and volume?

   [1 mark]

   • Adensity = volume / mass
   • Bdensity = mass / volume
   • Cdensity = mass x volume
   • Ddensity = mass + volume

   (b)

   If a second sample of the same oil had twice the volume of the first sample, what would its mass be, assuming both samples have the same density?

   [1 mark]

   • ATwice as much
   • BHalf as much
   • CThe same
   • DFour times as much

   (c)

   Calculate the density of the olive oil sample, in kg/m3.

   [2 marks]

   Total for question 5: 4 marks

6. 6
   A candle maker pours melted wax into moulds and leaves the wax to cool and set. A thermometer records the temperature of a 0.4 kg batch of the liquid wax as it cools from 70 degC. The wax fully solidifies at a constant temperature of 55 degC, and its specific heat capacity in the liquid state is 2100 J/(kg degC).

   (a)

   Which statement correctly describes what happens to the particles of the wax as it solidifies?

   [1 mark]

   • AThe particles move further apart and move faster
   • BThe particles remain in exactly the same arrangement, only slower
   • CThe particles gain kinetic energy and escape from the surface
   • DThe particles move closer together and become arranged in a fixed, regular pattern

   (b)

   While the wax is solidifying at a constant 55 degC, what is happening to the energy being removed from it by the surroundings?

   [1 mark]

   • AIt is reducing the kinetic energy of the particles, lowering the temperature
   • BIt has no effect since energy cannot be removed during solidifying
   • CIt is being removed from the store associated with the bonds between particles, so no temperature change occurs
   • DIt converts directly into light energy

   (c)

   Calculate the energy released by the 0.4 kg of liquid wax as it cools from 70 degC to 55 degC, just before it begins to solidify.

   [2 marks]

   Total for question 6: 4 marks

7. 7
   A bicycle repair shop mechanic uses a hand pump to compress air before transferring it into a tyre. At the start of a stroke, the air trapped inside the pump's cylinder has a volume of 480 cm3 at a pressure of 100 kPa. The mechanic then pushes the piston in, compressing the same mass of air to a volume of 120 cm3, while its temperature stays constant.

   (a)

   Explain, in terms of the motion of the air molecules, why compressing the air to a smaller volume at constant temperature increases its pressure.

   [3 marks]

   (b)

   Calculate the pressure of the air once it has been compressed to a volume of 120 cm3.

   [4 marks]

   Total for question 7: 7 marks

8. 8
   A hot-air balloon pilot heats the air inside the balloon's envelope using a gas burner before take-off. The envelope is open at its base, so heated air can escape freely, but once fully inflated its overall volume stays roughly the same. The heated air inside the envelope ends up at a lower density than the cooler air surrounding the balloon.

   (a)

   Explain, in terms of the motion and spacing of the air molecules, why the heated air inside the balloon's envelope ends up at a lower density than the cooler air outside, given that some of the warmed air escapes from the open base as the envelope is heated.

   [6 marks]

   (b)

   Suppose instead the base of the envelope were sealed shut, trapping a fixed mass of air at a fixed volume inside. Explain, using the kinetic theory of gases, what would happen to the pressure of the trapped air as the burner continued to heat it, and explain why this would be dangerous for the envelope's fabric.

   [6 marks]

   Total for question 8: 12 marks

End of questions