DP Physics (last assessment 2024)

Question 20N.2.HL.TZ0.1b

Date	November 2020	Marks available	[Maximum mark: 2]	Reference code	20N.2.HL.TZ0.1b
Level	HL	Paper	2	Time zone	TZ0
Command term	Calculate	Question number	b	Adapted from	N/A

[Maximum mark: 2]

20N.2.HL.TZ0.1b

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 $1.7 kg$ .

(b)

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]

Markscheme

vertical force = lift force – weight OR $= 0.45 \times 9.81$ OR $= 4.4 « N »$ ✓

acceleration $= \frac{0.45 \times 9.81}{0.95} = 4.6 « {ms}^{- 2} »$ ✓

Examiners report

Well done by a good number of candidates. Many earned a mark by simply using the correct mass to find an acceleration even though the force was incorrect.

Syllabus sections

Core

Core » Topic 2: Mechanics » 2.2 – Forces

Core » Topic 2: Mechanics

Question 20N.2.HL.TZ0.1b

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