khalizo123
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Peter aims straight across the river, and is carried downstream by the current.
i How long does he take to reach the other side?
il Work out his actual speed of travel. b Mary swims to the closest point on the opposite bank.
i In which direction does she aim? ii Work out her actual speed of travel.
ili How long does it take her to reach the other side?
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old_engineer
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(Original post by khalizo123)
Peter aims straight across the river, and is carried downstream by the current.
i How long does he take to reach the other side?
il Work out his actual speed of travel. b Mary swims to the closest point on the opposite bank.
i In which direction does she aim? ii Work out her actual speed of travel.
ili How long does it take her to reach the other side?
There must be a diagram and/or some additional information that goes with this question, like the width of the river, the speed of the current and the speed with which the two people can swim through the water.
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khalizo123
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(Original post by old_engineer)
There must be a diagram and/or some additional information that goes with this question, like the width of the river, the speed of the current and the speed with which the two people can swim through the water.
here it is
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khalizo123
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(Original post by khalizo123)
here it is
A river flows at 0.3 ms. Peter and Mary, who can each swim at 0.5 ms' in still water, wish to cross the river. The river is 20 metres wide.Peter aims straight across the river, and is carried downstream by the current.
i How long does he take to reach the other side?
il Work out his actual speed of travel. b Mary swims to the closest point on the opposite bank.
i In which direction does she aim? ii Work out her actual speed of travel.
ili How long does it take her to reach the other side?
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old_engineer
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(Original post by khalizo123)
A river flows at 0.3 ms. Peter and Mary, who can each swim at 0.5 ms' in still water, wish to cross the river. The river is 20 metres wide.Peter aims straight across the river, and is carried downstream by the current.
i How long does he take to reach the other side?
il Work out his actual speed of travel. b Mary swims to the closest point on the opposite bank.
i In which direction does she aim? ii Work out her actual speed of travel.
ili How long does it take her to reach the other side?
OK, so what have you tried, and where are you stuck?
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khalizo123
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idk how to do it

(Original post by old_engineer)
OK, so what have you tried, and where are you stuck?
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old_engineer
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(Original post by khalizo123)
idk how to do it
For part (i), Peter is swimming in a direction straight across the river. He is swimming perpendicular to the current, so the current does not affect his progress in the direction across the river. He is swimming at 0.5m/s and has to cover 20m. So how long does it take?
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khalizo123
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40s

(Original post by old_engineer)
For part (i), Peter is swimming in a direction straight across the river. He is swimming perpendicular to the current, so the current does not affect his progress in the direction across the river. He is swimming at 0.5m/s and has to cover 20m. So how long does it take?
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old_engineer
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(Original post by khalizo123)
40s
Yes. Now for part (ii) he is moving at 0.5m/s across the river and 0.3m/s down the river, with the current. That's two components of velocity at right angles to one another. So what is his speed across the ground?
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khalizo123
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idk could u give me a formula
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old_engineer
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(Original post by khalizo123)
idk could u give me a formula
It's basically Pythagoras. You need to learn about adding perpendicular vectors and finding the magnitude of the resultant vector before proceeding further with this question.
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