In the picture below, the speed of the boat with respect to the water is 4 mph (

Question

In the picture below, the speed of the boat with respect to the water is 4 mph (4 miles per hour), and the current is 3 mph (3 miles per hour). Imagine that the river is exactly 1 mile wide.

8. How much time does the boat (b) need to cross the river?
9. How far downstream from the starting point will the boat (b) reach the other shore?
10. The skipper wants to reach the other shore at a point exactly across the river from the starting point, so he has to steer as shown in (a). Will the time of crossing increase, decrease, of remain unchanged? p 79 conceptual physics, 11 edition #4 is diagram to use

Explanation / Answer

a)t=d/v=1/4hour=0.25 hour=15minutes=900s

b)distance downstream=vx*t=3*0.25miles=0.75miles.

c)To reach the exactly opposite point, the tangential component of the boat's speed should cancel that of the current. Therefore, the component normal to current is lower than in first case.

Therefore, it takes a longer time to cross.

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