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!

More force problems

  1. Jul 12, 2007 #1
    [SOLVED] more force problems

    1. The only two forces acting on a body have magnitudes of 20 N and 36 N and directions that differ by 72°. The resulting acceleration has a magnitude of 20 m/s2. What is the mass of the body?

    2. F=ma

    3. My original attempt was to add the two force magnitudes and divide by the acceleration magnitude, but I knew that wasn't right. I tried breaking up the force magnitudes up into x,y components, but that didn't seem to work either. So I'm pretty clueless. I'm having a hard time understanding this chapter so far. Hints to point me in the right direction would be great. Thanks.
  2. jcsd
  3. Jul 12, 2007 #2


    User Avatar
    Homework Helper

    You can't just add the magnitudes together.

    Try using vector addition and some trig to find the magnitude of the resultant force.
  4. Jan 17, 2008 #3
    Let's determine that 36N is on x-axis. Then find x and y components of 20N, which is 20cos(72) and 20sin(72).
    Add the x components and 36N together because both are on same direction and axis.
    Find magnitude of the force by use pyth. theorem.
    Then apply it to Newton's second law, F=ma. Then divide the acceleration, 20 m/s^2, and you will get the mass of the body.
  5. Jan 17, 2008 #4

    Shooting Star

    User Avatar
    Homework Helper

    No need to break up into x and y components this time. You need only the magnitude.

    R^2 = P^2 + Q^2 + 2PQcos(theta), where R is the resultant.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: More force problems
  1. More Force Review! (Replies: 3)