O-LevelPhysicsThermal Physics5054/21 · May/June 2018 · Q36 Marks

A passenger in an aircraft closes a plastic bag with some air inside, as shown in Fig. 3.1. [Figure 3.1]

(a)Explain how the molecules of air in the bag exert a pressure on the inside of the bag.[2]
(b)(i)When the bag is closed, the pressure of the air inside the aircraft is 80kPa and the bag contains 500 cm³ of air. When the aircraft is on the ground, the pressure of the air inside the aircraft is 100 kPa. Calculate the volume of air inside the bag when the aircraft is on the ground. volume = ................................................................[2][2]
(b)(ii)State two assumptions that you made in your calculation in (b)(i). 1. 2.[2]

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Mark scheme

Marking points from the official mark scheme (May/June 2018). The mark or mark type is shown in brackets.

[B1] they / molecules hit (inside) wall
[B1] they / molecules create a force and a reference to area
[C1] P1V1 = p2V2 in any form numerical or algebraic
[A1] 400 cm³
[B2] ANY 2 from • no gas / air / molecules escape(s) • temperature constant • no forces between molecules

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