260 Linear Momentum and CollisionsP9.24Energy is conserved for the bob-Earth system between bottom andtop of swing. At the top the stiff rod is in compression and the bobnearly at rest.KUK Uiiff+= +:120022MvMgb+=+Avgb24=Aso b=2AMomentum of the bob-bullet system is conserved in the collision:mvmvMg=+22AejvMmg=4AFIG. P9.24P9.25At impact, momentum of the clay-block system is conserved, so:mvmm v1122bgAfter impact, the change in kinetic energy of the clay-block-surfacesystem is equal to the increase in internal energy:12120 1120 650 0 1129 807 50122222mmv fd mmgdvf+==+=afµ.....kgkgm sm2v2295 6=. m s22v2977=. ms12 0 100 1129 7731.×=−kgkgm sbgvv191 2=. msFIG. P9.25P9.26We assume equal firing speeds vand equal forces Frequired for the two bullets to push wood fibersapart. These equal forces act backward on the two bullets.
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