CHAPTER 6. MOTIONIN TWO DIMENSIONS 6.5
30 ◦
A
Q
P
100 m
River
current
N
E
S
�
�
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During the swim, Andrew maintains a constantvelocity of 1,5 m.s−^1
East relative to the water. The water in the river flows at a constant
velocity of 2,5 m.s−^1 in a direction 30◦North of East. The width of
the river is 100 m.
The diagram below is avelocity-vector diagramused to determine the
resultant velocity of Andrew relative to the riverbed.
A B
C
(a) Which of the vectors(AB, BC and AC) refer toeach of the follow-
ing?
i. The velocity of Andrew relative to the water.
ii. The velocity of the water relative to the waterbed.
iii. The resultant velocity of Andrew relative to the river bed.
(b) Determine the magnitude of Andrew’s velocity relative to the
river bed either by calculations or by scale drawing, showing
your method clearly.
(c) How long (in seconds) did it take Andrew tocross the river?
(d) At what distance along the river bank (QP) should Peter wait with
Andrew’s bicycle readyfor the next stage of therace?
- [IEB 2002/11 HG1- Bouncing Ball]
A ball bounces vertically on a hard surface after being thrown verti-
cally up into the air by aboy standing on the ledge of a building.
Just before the ball hitsthe ground for the first time, it has a velocity
of magnitude 15 m.s−^1. Immediately, after bouncing, it has a velocity
of magnitude 10 m.s−^1.
The graph below showsthe velocity of the ball as a function of time
from the moment it is thrown upwards into the air until it reaches its
maximum height after bouncing once.
