6.5 CHAPTER 6. MOTIONIN TWO DIMENSIONS
(b) Calculate their average velocity, in km·hr−^1 , in which the aero-
plane should be travelling in order to reach Johannesburg in the
prescribed 5 hours. Include a labelled, rough vector diagram in
your answer.
(If an accurate scale drawing is used, a scale of25 km·hr−^1 = 1
cm must be used.)
- Niko, in the basketof a hot-air balloon, isstationary at a height of
10 m above the level from where his friend, Bongi, will throw a ball.
Bongi intends throwingthe ball upwards and Niko, in the basket,
needs to descend (move downwards) to catch the ball at its maximum
height.
�� �
13 m· s−^1
10 m
Bongi throws the ball upwards with a velocity of13 m·s−^1. Niko starts
his descent at the sameinstant the ball is thrown upwards, by letting
air escape from the balloon, causing it to accelerate downwards. Ig-
nore the effect of air friction on the ball.
(a) Calculate the maximum height reached by the ball.
(b) Calculate the magnitude of the minimumaverage acceleration
the balloon must havein order for Niko to catch the ball, if it
takes 1,3 s for the ball toreach its maximum height.
- Lesedi (mass 50 kg)sits on a massless trolley. The trolley is travelling
at a constant speed of 3m·s−^1. His friend Zola (mass60 kg) jumps
on the trolley with a velocity of 2 m·s−^1. What is the final velocity of
the combination (Lesedi, Zola and trolley) if Zolajumps on the trolley
from
(a) the front
(b) behind
(c) the side
(Ignore all kinds of friction)
