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Date	November 2020	Marks available	3	Reference code	20N.2.SL.TZ0.1
Level	Standard level	Paper	Paper 2	Time zone	0 - no time zone
Command term	Determine	Question number	1	Adapted from	N/A

Question

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 $1.7 kg$ .

State the value of the resultant force on the aircraft when hovering.

[1]

a(i).

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

[2]

a(ii).

Determine $v$ . State your answer to an appropriate number of significant figures.

[3]

a(iii).

The package and string are now released and fall to the ground. The lift force on the aircraft remains unchanged. Calculate the initial acceleration of the aircraft.

[2]