Consider a swimmer who wants to swim directly across a river as shown in the figure below. If the speed of the current is 0.29 m/s and the swimmer's speed relative to the water is 0.64 m/s, how long will it take her to cross a river that is 14 m wide?

Answer 1

draw the velocity diagram. I assume the figure has him swimming slightly upstream and the current is keeping him in a straight across path.

His velocity upstream/relative water+ velocity of water=his resultant velocity
But these are vectors, and it is a right trianagle.

.64^2=hisvelocity^2 + current^2
hisvelocity^2=.64^2-.29^2

his velocity across= sqrt .3225 check that.

his velocity=.571 m/s

time across= distance/velocityabove
= 14/.572=24.5 seconds

check the math.