DP Physics (last assessment 2024)

Question 20N.2.HL.TZ0.1a(iii)

Date	November 2020	Marks available	[Maximum mark: 3]	Reference code	20N.2.HL.TZ0.1a(iii)
Level	HL	Paper	2	Time zone	TZ0
Command term	Determine	Question number	a(iii)	Adapted from	N/A

a(iii).

[Maximum mark: 3]

20N.2.HL.TZ0.1a(iii)

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 $1.7 kg$ .

(a(iii))

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

[3]

Markscheme

«lift force/change of momentum in one second» $= 1.7 v$ ✓

$1.7 v = (0.95 + 0.45) \times 9.81$ ✓

$v = 8.1 « {ms}^{- 1} »$ AND answer expressed to $2$ sf only ✓

Allow $8.2$ from $g = 10 m s^{- 2}$ .

Examiners report

This was answered well with many getting full marks. A small number gave the wrong number of significant figures and some attempted to answer using kinematics equations or kinetic energy.

Syllabus sections

Core

Core » Topic 2: Mechanics » 2.4 – Momentum and impulse

Core » Topic 2: Mechanics

Question 20N.2.HL.TZ0.1a(iii)

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