Results 1 to 2 of 2

Math Help - forces

  1. #1
    Senior Member furor celtica's Avatar
    Joined
    May 2009
    Posts
    271

    forces

    a block of mass 20kg is held in equilibrium on a plane by means of a string which is at an an angle of 25 to the greatest slope of the plane. the plane is at 40 to the horizontal.
    show that the tension in the string is about 142N
    i thought this would be pretty straightforward but i just don't get 142N! i mostly used 200cos60 = Tcos25 but this doesn't wrok, why? are there forces i am missing? no friction btw
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    Opalg's Avatar
    Joined
    Aug 2007
    From
    Leeds, UK
    Posts
    4,041
    Thanks
    7
    Quote Originally Posted by furor celtica View Post
    a block of mass 20kg is held in equilibrium on a plane by means of a string which is at an an angle of 25 to the greatest slope of the plane. the plane is at 40 to the horizontal.
    show that the tension in the string is about 142N
    i thought this would be pretty straightforward but i just don't get 142N! i mostly used 200cos60 = Tcos25 but this doesn't wrok, why? are there forces i am missing? no friction btw
    The forces acting on the block are (1) its weight (vertically downwards), (2) the tension T in the string (at an angle 25 to the plane), (3) the normal force N supporting the block on the plane (acting perpendicular to the plane because we're assuming there's no friction).

    To calculate T, resolve the forces in the direction of the slope of the plane. Then the effect of N is eliminated, the weight makes an angle 50 (not 60!) to this direction, and the tension makes an angle 25. So the equation is 200\cos50^\circ = T\cos25^\circ.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. forces 2
    Posted in the Calculus Forum
    Replies: 2
    Last Post: February 20th 2010, 10:32 AM
  2. forces again
    Posted in the Math Topics Forum
    Replies: 1
    Last Post: July 2nd 2009, 06:42 AM
  3. Forces
    Posted in the Pre-Calculus Forum
    Replies: 1
    Last Post: March 11th 2009, 02:40 PM
  4. Forces
    Posted in the Advanced Applied Math Forum
    Replies: 1
    Last Post: December 23rd 2008, 07:15 AM
  5. forces
    Posted in the Trigonometry Forum
    Replies: 13
    Last Post: July 10th 2008, 07:46 AM

Search Tags


/mathhelpforum @mathhelpforum