1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Power problem

  1. May 16, 2014 #1
    1. The problem statement, all variables and given/known data
    A speedboat requires 130 hp move at a constant speed of 15 m/s. Calculate the resistive force due to the water at that speed.


    2. Relevant equations
    P=F(V)


    3. The attempt at a solution
    I attempted to use Newtons first law that says in order for a object to be at rest the sum of the forces must be zero. Therefore I thought that the horsepower for the force of friction must be the same as the propulsion. So
    130=F(15)
    F= 8.6
    The answer is 6.47x10^3 N or 1450 lbs
     
  2. jcsd
  3. May 16, 2014 #2

    SammyS

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    The problem is with the units.

    Horsepower is not an SI unit.
     
  4. May 17, 2014 #3
    F = 8.6 what??? What are the units? You forgot to convert the units to some consistent system. hp is a British unit while m/s is International.
     
  5. May 17, 2014 #4

    Curious3141

    User Avatar
    Homework Helper

    There's a standard conversion from hp to kW that every petrolhead will be familiar with. Use that conversion (google it) and work purely in SI units.
     
  6. May 17, 2014 #5
    OK I see what I did and found out how to solve the problem. Thanks everyone!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Power problem
  1. Power problem (Replies: 1)

  2. Problem on Power! (Replies: 0)

  3. Power Problem (Replies: 1)

  4. Power problem (Replies: 7)

Loading...