Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Find the power an electric motor

  1. Sep 15, 2004 #1
    hi, i need just a formula to go ahead with this. I am given two masses, m1 of man, and m2 of his bike. he is going up a hill with slope (sqroot3/3) and velocity (v). Now I need to find the power an electric motor would need to have for the man to b able to ride his bike up without pedalling.
    Power = energy / time, right? how can i find the time? pls help urgently!! :uhh:
  2. jcsd
  3. Sep 15, 2004 #2
    1) First, you must find the angle that the hill makes. Actually, you might be able to skip this step, but I couldn't and still logically produce the rest of the equation.

    2) Secondly, find the acceleration on the bike.

    3) Now you know the force (since you know the mass and acceleration), you can find the work involved in moving the bike any incremental distance.

    4) To find the power, substitute velocity for distance in the work equation.

    I believe this will provide you with the correct answer.
  4. Sep 15, 2004 #3
    I just thought of another way to look at this:

    Assuming these variable are constant enough for an integral to be a multiple,

    Work is force times distance.

    Velocity is distance divided by time.

    Power is work divided by time. Therefore Power is force times distance divided by time.

    This type of thinking ONLY works because force and velocity are constant. Since they are, though, it works :tongue2:
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook