1. Not finding help here? Sign up for a free 30min 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!

Tension Rope and Blocks Problem

Tags:
  1. Apr 11, 2015 #1
    1. The problem statement, all variables and given/known data
    Two blocks, each with weight w, are held in place on a frictionless incline as shown in Figure. In terms of w and the angle a of the incline, calculate the tension in the rope connecting the blocks
    chemistry_8f635c0b85d41ce64d978925fca6415e.jpg
    2. Relevant equations
    T = mg

    3. The attempt at a solution
    I cannot for figure out why the answer is Wsin(a)! I thought that since Tsin(a) = mg, T = w/sin(a)
     
  2. jcsd
  3. Apr 11, 2015 #2
    You have to look at the forces that are pulling along the surface. The force pulling downwards the slope is ##F_d=mgsin(a)##, the force pulling up is just the tension ##T##. For the block to be not moving along the slope these two have to be equal to eachother.
     
  4. Apr 11, 2015 #3

    gneill

    User Avatar

    Staff: Mentor

    Hi DaveTan, Welcome to Physics Forums.

    Take a close look at the geometry of a block on a slope. The weight W = Mg forms the hypotenuse of the force triangle:

    Fig1.gif
     
  5. Apr 12, 2015 #4
    Thanks! But shouldn't tension be pointing in the other direction? So towards the top-right instead of bottom left?
     
  6. Apr 12, 2015 #5

    haruspex

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    Tension acts both ways (as does compression). The force it exerts on B will be up and to the right, that on A down and to the left.
    By the way, the reason your original approach went wrong is that the vertical forces include a component of the normal force.
     
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: Tension Rope and Blocks Problem
Loading...