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: Box on an inclined plane

  1. Nov 2, 2013 #1
    I am stuck on a problem from the 5 Steps to a 5: AP Physics B&C book and would really appreciate anyone's help.

    1. The problem statement, all variables and given/known data
    Determine (a) the acceleration of the block down the plane and (b) the time for the block to slide to the bottom of the plane.

    http://02.edu-cdn.com/files/static/mcgrawhillprof/9780071623209/INCLINED_PLANES_08.GIF [Broken]

    2. Relevant equations
    F, gravity = mg
    F, friction = umg
    Kinematic equation ???

    3. The attempt at a solution

    Fx, up the plane = mgsin25 + umgcos25 = 204 N
    a = F/m = 204/30 = 6.8 m/s^2
    Fx, down the plane = mgsin25 - umgcos25 = 44 N
    a = F/m = 44/30 = 1.5 m/s^2

    I tried using x = Vot + 1/2 at^2 (x = 20 m, Vo = 3m/s) and v = Vo + at (v = 0, Vo = 3 m/s) to solve for time, but my answers were way off on both attempts.
    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. Nov 3, 2013 #2
    If the question says the mass is going 3 m/s up the plane, and the a) part asks for the acceleration DOWN the plane this means that x != 20, but it is going to be 20 added to the distance travelled by the mass until it changes direction. I hope that helped.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted