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!

Homework Help: Can someone explain a simple physics question for me?

  1. Nov 5, 2009 #1
    Okay this isn't really a problem, but I want it explained too me instead of the books way. We are doing a section on mechanical energy, and for the entire course with vectors, force, etc, we have always used rcostheta and rsintheto to find an x and y force.

    Now tell me why we do this? Is this to elimate the forces from a vector component form to a basic x y form, where y is a 90 degree value, and x is a 0 degree value?

    Also another question. We used the equation for change in mechanical energy where energy potential, and kinetic energy where the same regardless of its position along a path when looking at conservative forces.

    I used rcostheta and rsintheta to plug in values for velocity when they where at angles, but I noticed that this data does not accurately give the TOTAL potential energy correctly.

    To use an example say that

    a ball is fired at 600m/s at 30 degrees with a mass of 24kg.

    To plug this into the isloated system model for velocity I had to use velocity x sin30

    but when it asked for its total mechanical energy at the balls maximum height I used 1/2mvf^2 and just plugged in 600.
  2. jcsd
  3. Nov 5, 2009 #2


    User Avatar
    Gold Member

    Please use the question template provided.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook