River Speed Calculations for Relativity

[kraaaaamos]

Homework Statement

A boat traveling with the current has a speed of 10km/h.
The same boat travels against the same current at the speed of 6km/h.
At what speed is the river flowing?

Homework Equations

The Attempt at a Solution

10km/h - 6km/h = 4km/h ?

 

[learningphysics]

No. That's not right.

If the speed of the boat is b, and the speed of the river is r... what is the speed of the boat traveling with the river in terms of b and r... equate this to 10.

this gives 1 equation..

what is the speed of the boat traveling against the river in terms of b and r... equate this to 6.

this gives a 2nd equation... so you have 2 equations with 2 unknowns.

solve for r speed of the river.

 

[kraaaaamos]

how do i do that? = S

 

[Dick]

Do what learningphysics suggested. If the speed of the boat is b and the speed of the river is r, they add and give 10 if they are going in the same direction. They subtract and give 6 if they are going in opposite directions. Write down those two equations. And then solve them.

 

[kraaaaamos]

b + r = 10, b = 10-r
b - r = 6

10-r-r = 6
10-2r = 6
4 = 2r
r = 2 ?

: )

 

[Dick]

r=2. That says it all.

 

[learningphysics]

Yup r = 2 km/hr is the answer.