Time for boat to make two sets of displacements

[Maiia]

Homework Statement

I would really appreciate if someone could check my work for this poblem b.c i seem to be getting the wrong answer.

Problem: A boat moves through a river at 6.1 m/s relative to the water, regardless of the boat's direction. If the water in the river is flowing at 2.4 m/s, how long does it take the boat to make a round trip consisting of a 246 m displacement downstream followed by a 194 m displacement upstream? Answer in units of seconds.

First, I used the pythagorean theorem to find the resultant vector- 6.555150647m/s. Then, used distance=Velocity * time . I plugged in 246m for distance and 2.4m/s for the velocity to get 102.5 sec for time. I did the same thing with the second displacement to get 183.3333333s for time. Then I added them together for a total time of 183.3333333s.

 

[madmike159]

If its going down stream then up stream surly that means its going from A to B and then B to A.
If its moving 6.1m/s relative to the water down stream it would be moving at 8.5m/s
up stream it would be moving at 3.7m/s (unless it is taking 6.1m/s as its actual velocity, but then why would you have the speed of the water?).

 

[Maiia]

hmm i kinda follow, but how do you find the time?

 

[madmike159]

With distance = velocity * time. If your having trouble with the boat moving relative to the water think of trying to measure the speed of a car from inside another moving car. If you were measuring car A (30mph) from car B (20mph) it would look like car A is going 10mph.