Question

A boat can travel at 13m/s in still water. It has to travel across a stream which is 78m wideand flowing at where is the unit vector along the straight banks. How long will the crossing take 1) By the quickest route? 2) By the shortest route?

Answer 1

The velocity of river is??

Answer 2

not given

Answer 3

So, no answer i guess.

Answer 4

@DLS they're right. u can't solve this question unless u know the velocity of river.

Answer 5

@ujjwal won't the quickest and the shortest route both be the same?

Answer 6

http://www.wiziq.com/tutorial/19847-Relative-Velocity
6th slide

Answer 7

which is going straight towards the other bank. not at an angle.

Answer 8

ah! river's velocity is given = 5m/s^2

Answer 9

i mean m/s

Answer 10

oh sorry :o i copied from the text given bellow,its a pic there so yeah :o

Answer 11

Where is it? I still don't see..

And @Vaidehi09, I too thought the same way. Shortest and quickest route should be same. But i am not 100% sure.

Answer 12

I'm sure they are the same. Just checked in H.C.Verma.

Answer 13

Oh, He is a great writer. I have heard a lot about his book.

Answer 14

yup. his books are easy to study from. detailed to the core concept.

Answer 15

why same?

Answer 16

see, shortest route is straight up. the quickest is also the same.
now, the boat can move at speed 13m/s in still water. that is its max speed limit. now, if he starts moving at an angle A with the vertical, the its vertical component of speed will become 13cosA, right? and this less than 13. so, considering the vertical motion, its speed has decreased. so it'll take longer to cover the width of the river.