physics
posted by Kara .
A boat takes 3hr to travel 30 km down a river, then 5hr to return. How fast is the river flowing?

physics 
drwls
Let V = stream velocity and v = boat velocity with respect to water. Both are in km/hr.
3 hr = 30/(V + v)
5 = 30/(V v)
Solve those two equations in two unknowns for V and v.
5(V v) = 3(V +v)
2V = 8v
v = V/4
3 = 30/(5V/4)= 120/5V
15V = 120
etc
Respond to this Question
Similar Questions

Physics
A boat takes 2.70 hours to travel 40.0 km down a river, then 5.90 hours to return. How fast is the river flowing? 
Physics
A boat takes 2 hours to travel 30 km down a river, then 6.5 hours to return. How fast is the river flowing? 
physics
You are riding in a boat whose speed relative to the water is 4.7 m/s. The boat points at an angle of 24.4° upstream on a river flowing at 13.1 m/s. Find the time it takes for the boat to reach the opposite shore if the river is 25.9 … 
physics
You are riding in a boat whose speed relative to the water is 4.7 m/s. The boat points at an angle of 24.4° upstream on a river flowing at 13.1 m/s. Find the time it takes for the boat to reach the opposite shore if the river is 25.9 … 
physics
You are riding in a boat whose speed relative to the water is 6.9 m/s. The boat points at an angle of 25.0° upstream on a river flowing at 15.1 m/s. Find the time it takes for the boat to reach the opposite shore if the river is 26.5 … 
physics
You are riding in a boat whose speed relative to the water is 4.5 m/s. The boat points at an angle of 25.1¡ã upstream on a river flowing at 12.8 m/s. Find the time it takes for the boat to reach the opposite shore if the river is … 
math
The current river flows at rate of 4mph. In order for a boat to travel 24 miles up river and then return in a total of 5 hours how fast must the boat be able to travel in still water? 
physics
You are riding in a boat whose speed relative to the water is 7.4 m/s. The boat points at an angle of 24.8° upstream on a river flowing at 15.2 m/s. Find the time it takes for the boat to reach the opposite shore if the river is 26.1 … 
math
It takes Ashley 8 hours to kayak 18 km up river and 18 km back down the river. if the river is flowing at 3 km/h, how fast did she puddle assuming she paddled at a constant speed? 
physics
A boat is heading directly North acroos a river at 5km\h. The river is flowing east at 3km\h. a) what is the actual velocity of the boat?