With what force must you pull?

The tune-up specifications of a car call for the spark plugs to be tightened to a torque of 38 N * m. You plan to tighten the plugs by pulling on the end of a 25-cm-long wrench. Because of the cramped space under the hood, you’ll need to pull at an angle of 120 degrees with respect to the wrench shaft. With what force must you pull?

forgetting the angle for the moment,

38 N-m /.25m = 152 N that you need to pull on, at right angles to the wrench.

120º to the shaft is 30º to the perpendicular, so your force is reduced by F’ = Fcos30 = F*0.866

Thus the total force you have to apply is 152N / 0.866 = 196 N

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