A river is flowing at a uniform velocity of v = 1 0 m/s . As shown in the diagram, P , Q , and R are three points on a line perpendicular to the river such that P Q = Q R = 1 0 0 m .
A boat starts from point P and moves at a constant speed of v = 1 0 m/s relative to the river. It moves in such a way that the direction of its resultant velocity is always perpendicular to the line joining the boat and point R .
If the boat drifts a meters and takes b seconds to land on point S , submit your answer as a + b to 3 decimal places.
P.S If you liked this problem, check this one out too!!!
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Awesome!!....Hua nhi mjhse😂
Did it the same way. At first, I guessed the trajectory to be a circle, and immediately concluded it to be 2 0 0 , but even after getting the right solution, I wanted to prove it!
Same here too!
Since the resultant velocity is always perpendicular to the line joining the boat and R , the boat is moving in a circle of radius 2 w .
1) Thus the drift will be Q S = 4 w 2 − w 2 = 3 w
2) Suppose at any arbitrary time, the boat is at point B .
V n e t = 2 v cos θ
d t d θ = 2 w V n e t = w v cos θ
Cross multiplying :-
v w sec θ d θ = d t
Now integrating and using proper limits(at time t = 0 , the line joining R and P makes an angle of 0 ∘ , and at time t , the angle becomes 6 0 ∘ )
∫ 0 t d θ = v w ∫ 0 6 0 ∘ sec θ d θ
t = v w [ l n ( sec θ + tan θ ) ] 0 6 0 ∘
t = v 1 . 3 1 7 w
So adding them we get :-
[ ( 1 . 3 1 7 ) ( 1 0 ) + 3 ] ( 1 0 0 )
= 1 8 6 . 3 7 5
P.S If someone could pls help me with this solution by providing an image, it would be really great as it may prove to be difficult to deduce what angle is θ and some of the other things too.
ok will image in paint will be fine??
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Yup.All I need is an image which labels all the points and angles mentioned in my solution.Thank you
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ok when ever i get free time i will make it
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@Nivedit Jain – Thanks. I do hope there was a better way........
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@Pranav Saxena – which way is in your mind?? PLzzz share
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@Nivedit Jain – A better way so as to make images. Paint seems tiresome......... and making them in word and then converting them to jpg is also a lot of work.........
@Pranav Saxena Why have you taken θ as 60°?
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.When the boat reaches the opposite shore, it forms an equilateral triangle with the point R.Its difficult to convey this without an image..
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Very happy to solve this awsome problem,