While driving your car hits a pothole, blowing your front tire. Taking out your
ID: 1818389 • Letter: W
Question
While driving your car hits a pothole, blowing your front tire. Taking out your lug wrench (total span: 28 in), you try to loosen the lug nut, which requires 80 ft-lbf to turn. The only issue is that you are right-handed, and the force that you can exert with your left arm is 25% less than that of your right arm. Assume that you direct both forces along the y z plane.
a.) What is the minimum force that you need to apply with your right and left arm to turn the lug wrench and loosen the nut?
b.) How much easier would this job be if you had bought the more expensive lug wrench that featured a 36-in. span? State your answer in terms of the minimum force required from each arm.
Explanation / Answer
A.
since there's an angle, we only need the elment perpendicular to the arm: Frsin50=0.766Fr
Fl*sin50=0.766Fl=0.766*(3/4)*Fr=0.5745Fr
the total moment around the lug nut is:
0.766Fr*1.1666+0.5745Fr*1.1666=1.564Fr=80[ft lbf] ---> Fr=51.1507[lbf] //// 14inches=1feet 2inch =1.16667 feet
Fl=0.75Fr=0.75*51.1507=38.363 [lbf]
B.
sinc ehte arm turns from 14 inches to 18 inches=1.5[ft]:
(0.766F+0.5745F)*1.5=2.0109F =80 --> Fr=39.784[lbf]
Fl=0.75Fr=29.838[lbf]
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