Mary needs to row her boat across a 120 m -wide river that is flowing to the east at a speed of 1.4 m/s. Mary can row the boat with a speed of 2.0 m relative to the water.

Question

1. How long does it take Mary to reach the opposite river bank ?
2.If Mary rows straight north, how far downstream will she land?

Answer 1

Look at this in directions.
She rows North at 2.0m/s, and the distance is 120M North.
time= distanceN/speedN= 120m/2.0m/s=60sec

Where does she land. YOu have 2.0m/s across, downstream 1.4m/s

In 60 seconds, she goes distance=1.4*60 m