Halliday, Resnick & Walker — Force and Motion-II: Problem 12

12 In about 1915, Henry Sincosky of Philadelphia suspended himself from a rafter by gripping the rafter with the thumb of each hand on one side and the fingers on the opposite side (Fig. 6-19). Sincosky’s mass was 79 kg. If the coefficient of static friction between hand and rafter was 0.70, what was the least magnitude of the normal force on the rafter from each thumb or opposite fingers? (After suspending himself, Sincosky chinned him self on the rafter and then moved hand-over-hand along the rafter. If you do not think Sincosky’s grip was remarkable, try to repeat his stunt.)