356 Static Equilibrium and ElasticityP12.15(a)Taking moments about P,RRRsin.cos.....30 0030 05 0015030 001 039 21 04°+°−===afafaf afafcmNcmNkNThe force exerted by the hammer on the nail is equal in magnitudeand opposite in direction:1 04.kN at 60upward and to the right.°(b)fR=°−=sin.30 0150370NNnR=°==+cos.±±30 0900370900NNNsurfaceFijaf afFIG. P12.15P12.16See the free-body diagram at the right.When the plank is on the verge of tipping about point P, thenormal force n1goes to zero. Then, summing torques aboutpoint PgivesτpmgdMgx∑= −+=0orxmMd=FHGIKJ.From the dimensions given on the free-body diagram, observe
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