A boat moves directly across a river with speed 10 km h⁻¹ relative to water. The water flows uniformly at 5 km h⁻¹ relative to earth. The river is 3.0 km wide. How long does the boat take to cross?
Select all that apply

Question

A boat moves directly across a river with speed 10 km h⁻¹ relative to water. The water flows uniformly at 5 km h⁻¹ relative to earth. The river is 3.0 km wide. How long does the boat take to cross?

Select all that apply

G1 Physics · Accepted Answer

The component perpendicular to the banks is 10 km h⁻¹. The current changes only the downstream drift. Thus t=3/10 h=0.3 h=18 min. Hence option C.