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A boy and girl both swim at 3.0m/s. They jumpinto a river 1.0km across, with a current of 2.0m/s (E). She swims straight across relative to the shore. How long (in minutes) does each take to cross the river
 2 years ago
 2 years ago
A boy and girl both swim at 3.0m/s. They jumpinto a river 1.0km across, with a current of 2.0m/s (E). She swims straight across relative to the shore. How long (in minutes) does each take to cross the river
 2 years ago
 2 years ago

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shubhamBest ResponseYou've already chosen the best response.1
You are given the velocity of boy and girl w.r.t the ground and velocity of current w.r.t ground. Velocity of girl w.r.t ground, V(g,G) = 3 m/s Velocity of current = V (c,G) = 2 m/s Now, velocity of girl w.r.t current = V(g,G) + V(c,G) [ vector sum!! ] Hope you may try to solve it now...
 2 years ago

shubhamBest ResponseYou've already chosen the best response.1
No... I said the vector sum, as the direction of speeds are different you can't just add both the velocities..
 2 years ago

beth12345Best ResponseYou've already chosen the best response.0
oh would I use a squared +b squared = c squared
 2 years ago

shubhamBest ResponseYou've already chosen the best response.1
But, think.. For calculating time she required to cross the river if she propells herself perpendicular to the shore, would in anyway be affected by velocity of current.
 2 years ago

shubhamBest ResponseYou've already chosen the best response.1
Think why time depends on both components...
 2 years ago

beth12345Best ResponseYou've already chosen the best response.0
uhm, I don`t understand
 2 years ago

beth12345Best ResponseYou've already chosen the best response.0
dw:1331693378113:dw this is all I understand so far...
 2 years ago

shubhamBest ResponseYou've already chosen the best response.1
Right. See, She propells herself perpendicular to the bank at 3 m/s and at the same time she is getting pushed sideways at 2 m/s. So, her resultant velocity will be directed at an angle b/w the two.
 2 years ago

shubhamBest ResponseYou've already chosen the best response.1
Now, see 3m/s contributes to her getting across the bank. Time she requires = 1000 m / 3 m/s = 333.33 sec.
 2 years ago

beth12345Best ResponseYou've already chosen the best response.0
and then it makes an angle triangle like this dw:1331693918116:dw ?
 2 years ago

beth12345Best ResponseYou've already chosen the best response.0
and then it is 5.6 minutesÉ
 2 years ago

shubhamBest ResponseYou've already chosen the best response.1
RIght, you may shift vectors in a plane, without changing the directions and magnitude.
 2 years ago

beth12345Best ResponseYou've already chosen the best response.0
oh i think i get it, does the 2m per s affect it?
 2 years ago

shubhamBest ResponseYou've already chosen the best response.1
No, it doesn't effect the time, but other parameters like where she would land on the other bank does.
 2 years ago

beth12345Best ResponseYou've already chosen the best response.0
ok, is it the same for the boy then?
 2 years ago

shubhamBest ResponseYou've already chosen the best response.1
Yes, Gender doesn't effect the time as well.. lol..
 2 years ago

beth12345Best ResponseYou've already chosen the best response.0
oh right! haha well thanks for helping :)
 2 years ago
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