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: Incline Problem

  1. Jul 12, 2006 #1
    I have a question about this problem:

    "A block is given an initial velocity of 5.00 m/s up a frictionless 20.0(degrees) incline. How far up the incline does the block slide before coming to a rest?"

    The book gives a clue stating that mgx = -mgsin20.0 and mgy=-mgcos20.

    My question is why is mgx negative mgsin20?

    When I work it out:

    Sum of x force = mgsin20 = ma,
    therefore: a = gsin20

    Do they make it negative because the force of gravity in the x direction is going in a negative direction while the velocity is going in a positive direction?
     
  2. jcsd
  3. Jul 12, 2006 #2
    I think it's negative becouse they defined the the direction of the initial velocity as positive, and so becous it's slowing down (along both the x and the y axis) the accelaration and force have to be negative.
     
  4. Jul 12, 2006 #3
    What course are you taking? I'll be in the Clark building tomorrow. Taking my final exam :yuck:

    :rofl: Whats your major?

    Ans. Because gravity slows the block down as it slides up the incline.

    The correct spelling is "because" lenin. Nice name BTW, clever.
     
  5. Jul 12, 2006 #4
    Thank you.
     
  6. Jul 12, 2006 #5
    :rofl: I just noticed your red text, how appropriate,.......commie.
     
  7. Jul 12, 2006 #6
    Ah, both of your answers make sense. Thank you.

    The class I am taking is Engineering Physics I.
    I am a computer science major.

    Looks like cyrusabdollahi and I go to the same school. Nifty.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook