Available practice: 75 of 80 marks. Parts 3(b), 6(a)(i) await marking support. Scores cover available parts only.
(a)Using ideas about momentum, explain how the atoms of helium produce a force on the wall of the balloon.
Answer guidance
Using You must use the thing it names. An answer that reaches the right value another way may not score.
[3 marks]
A balloon filled with helium is used to lift measuring instruments high above the Earth. At ground level, the pressure of the helium in the balloon is 1.0 × 10⁵ Pa. The volume of the helium is 9.6 m³. The balloon is released and it rises quickly through the atmosphere. The volume of the helium increases. The temperature of the helium remains constant.
(b)(i)Explain why the pressure in the balloon decreases as the balloon rises. You should refer to helium atoms in your answer.
Answer guidance
Explain Give reasons, not just what happens. Each distinct reason is usually worth a mark.
[2 marks]
A balloon contains helium at a pressure of 1.0 × 10⁵ Pa with a volume of 9.6 m³ at ground level. As the balloon rises the volume increases at constant temperature.
(b)(ii)Calculate the pressure of the helium when its volume is 12 m³.
Answer guidance
Calculate Show your working. The method can earn marks even when the final value is wrong, and a bare answer often cannot.
