Chapter 9259P9.21(a), (b) Let vgand vpbe the velocity of the girl and the plankrelative to the ice surface. Then we may say that vvgp−isthe velocity of the girl relative to the plank, so that−=150.(1) But also we must have mvggpp+=0, since totalmomentum of the girl-plank system is zero relative to theice surface. Therefore45 01500., or =−333.Putting this into the equation (1) above gives−−=..or vp0346. msThen vg−=3 33 0 346115.afmsFIG. P9.21*P9.22For the car-truck-driver-driver system, momentum is conserved:pppp1212ii ff+= +:4 000880084 800kgm skgm skgbgbgbgej±±±iii+−=vfvf=⋅=25 6004800533kg m skg.For the driver of the truck, the impulse-momentum theorem isFpp∆tfi:Fii0120808skgm skgm sbgb g=×−178 103.±Non the truck driverFor the driver of the car,i8skgm skgm sbg−889 10
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