Hello there!(adsbygoogle = window.adsbygoogle || []).push({});

This problem is giving me a hard time and I thought maybe one of you could give me a hint:

"A ship is going upstream with a constant power P. Its speed [tex]V[/tex] is relative to the water and the water's speed [tex]U[/tex] is relative to the shore. The ship needs tp overcome a frictional force of [tex]F_r=cv^2[/tex] caused by the water which depends on its relativ speed. How big does v have to be so that the ship goes from A to B with the lowest energy consumption?"

Where I would start is that the ship needs at least the power which is neccesary to stay in the same place. Which would be

[tex] P=F_r x U = cU^2U=cU^3[/tex] and than in addition some extra power to go upstream. That would be [tex] P=F_r x (v-u)=c(V-U)^2 x (V-U)[/tex]. But from here, if it's really correct, I do not know how to continue :(

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: A ship going upstream and experiences a frictional force

**Physics Forums | Science Articles, Homework Help, Discussion**