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Question 20N.2.SL.TZ0.a(ii)

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Date November 2020 Marks available [Maximum mark: 2] Reference code 20N.2.SL.TZ0.a(ii)
Level SL Paper 2 Time zone TZ0
Command term Outline Question number a(ii) Adapted from N/A
a(ii).
[Maximum mark: 2]
20N.2.SL.TZ0.a(ii)

A company delivers packages to customers using a small unmanned aircraft. Rotating horizontal blades exert a force on the surrounding air. The air above the aircraft is initially stationary.

The air is propelled vertically downwards with speed v. The aircraft hovers motionless above the ground. A package is suspended from the aircraft on a string. The mass of the aircraft is 0.95 kg and the combined mass of the package and string is 0.45 kg. The mass of air pushed downwards by the blades in one second is 1.7 kg.

Outline, by reference to Newton’s third law, how the upward lift force on the aircraft is achieved.

[2]

Markscheme

Blades exert a downward force on the air ✓


air exerts an equal and opposite force on the blades «by Newton’s third law»
OR
air exerts a reaction force on the blades «by Newton’s third law» ✓


Downward direction required for MP1.

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