Calculating Force on Aircraft Carrier John F. Kennedy

[Exuro89]

Homework Statement

The aircraft carrier John F. Kennedy has mass 7.4*10^7kg. When its engines are developing their full power of 280000 hp, the John F. Kennedy travels at its top speed of 35 knots.

If 70% of the power output of the engines is applied to pushing the ship through the water, what is the magnitude of the force of water resistance that opposes the carrier's motion at this speed?

Homework Equations

P=F*v

The Attempt at a Solution

Not sure if I understand the question correctly. What I did was convert 35 knots into m/s which was 18.06m/s. I converted the power from hp to watts to get 208880000watts. I divided the watts by the velocity to get force. If this is correct, this would be the force of the boat and not the water correct? Would the resistance be the 30% that the force loses?

 

[Delphi51]

Apparently 30% of the power is lost in the drive train and propeller.
Take 70% of the power and use it in the formula to find F.

 

[Exuro89]

Alright so couldn't I just find the total from what I did above, then dividing the power by the velocity to get force and then multiple that by .3 to get teh water resistance? 70% is going forward while the other 30% is water resistance?

EDIT: Hmm that not correct.

I really don't know what I need to do. I found the power in watts, divided by the velocity in m/s and then that should be the power the ship is producing, in which 30% is lost to water resistance right?

 

[Exuro89]

Apparently 30% of the power is lost in the drive train and propeller.
Take 70% of the power and use it in the formula to find F.

Would this just mean that the force of water resistance is equal to the force of the ship?

 

[Delphi51]

Would this just mean that the force of water resistance is equal to the force of the ship?

Yes. Motion at constant speed, so acceleration is zero and the total force on the ship is zero.