Question

A boat, whose speed in still water is 1.96 m/s, must cross a W = 217 m wide river and arrive at a point D = 111 m upstream from where it starts, as shown in figure below.


To do so, the pilot must head the boat at a 42.9° upstream angle. What is the speed of the river's current?

Answer 1

The method above is perfect, though the calculation of time seems to have gone into the calculator wrong! 217/1.434 = 151 seconds. That will affect the last part of the calculation as well.

Answer 2

if u resolve the inital velocity

then u will get the vertical component to be 1.96*cos 42.9

= 0.732 * 1.96=1.434 m / s

time taken to cross = 217 / 1.434=151.32seconds

distance travelled in x direction = 111m

initial velocity in x direction = - 1.96 * sin 42.9 =
= -0.680 *1.96= - 1.33

disance = speed * time

d = (v of current + velocity of man) * time
111= (v - 1.33)* 151.32

v - 1.33 = 0.733
v= 1.33 + 0.73 = 2.063

Answer 3

is my answer correct now
??

Answer 4

I think that the 'initial velocity' in the x-direction should be positive, if you say that the distance travelled in the x-direction is positive. The current velocity is going against the boat, so that should come out as negative in the end.

Answer 5

ok ok but the method is correct right?

Answer 6

Yarp.