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vector calculations

Anybody know how to do these questions? I don't know how to draw diagrams of them and therefore I just can't seem to get my mind around it

1. find the time it takes a motor launch which moves through the water at 10kmh to travel across a river at right angles to the cureent which flows at 6kmh. the width of the river is 1.2km

2. two cars leave a road junction at the same time. car A travels nort at 45kmh and car b travels eat at 60 kmh. find the apparent speed and direction of B as seen by an observer in a
Original post by longsightdon
Anybody know how to do these questions? I don't know how to draw diagrams of them and therefore I just can't seem to get my mind around it

1. find the time it takes a motor launch which moves through the water at 10kmh to travel across a river at right angles to the cureent which flows at 6kmh. the width of the river is 1.2km

2. two cars leave a road junction at the same time. car A travels nort at 45kmh and car b travels eat at 60 kmh. find the apparent speed and direction of B as seen by an observer in a


for 2 you could plot the positions after convinient time periods as (x,y) pairs
e.g.
0h (0,0) (0,0)
1h (0,45) (60,0)
2h (0,90) (120,0)

the apparent speed of B as seen from A is the change in separation of the points over one hour, the direction is the bearing from the position of A to the position B at the same time.
Reply 2
Avatar for ZazenTree
ZazenTree
These are tricky to explain without a diagram - once you've mastered the diagrams they become much more straightforward. Google 'resultant vector' and this should shed some light on how to do these types of problems.

The answers i get for your question are: 1) 9 mins; 2) 75km/h at an angle of 127 degs clockwise of north

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