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: Magnitude of Force on Wrench

  1. Feb 21, 2013 #1
    You are installing a new spark plug in your car, and the manual specifies that it be tightened to a torque that has a magnitude of 45.0 N*m. Using the data in the figure below (L = 0.300 m and ? = 52.6°), determine the magnitude F of the force that you must exert on the wrench.
    chaning your spark plugs.png

    Relevant Equations
    T = F * d

    45 = F * cos 52.6º * 0.300m
    F = 246.96 N
  2. jcsd
  3. Feb 21, 2013 #2
    What if θ was zero? According to your formula, this would give a torque of Fd (because cos(0) = 1). But, if you look at the picture, if θ = 0, shouldn't the torque be 0 as well? You are just pulling straight out; this shouldn't turn the bolt at all.

    Hint: is θ really the angle between the force and the displacement?
  4. Feb 21, 2013 #3
    If θ=0, then the force would be 150N. θ isn't the angle between the force and displacement, but what am I looking for instead of 52.6°?
  5. Feb 21, 2013 #4
    Basically, you want the component of F that is PERPENDICULAR to the displacement. Personally, I wouldn't use cosine but sine. Draw a right triangle with theta, F, and d, and find an expression for the component of F pointing away from d.
  6. Feb 22, 2013 #5
    I figured out that the answer is 1.898102N
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook