257_Physics ProblemsTechnical Physics

257_Physics ProblemsTechnical Physics - Chapter 9 P9.21 259...

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Chapter 9 259 P9.21 (a), (b) Let v g and v p be the velocity of the girl and the plank relative to the ice surface. Then we may say that vv gp is the velocity of the girl relative to the plank, so that −= 150 . (1) But also we must have mv gg pp += 0, since total momentum of the girl-plank system is zero relative to the ice surface. Therefore 45 0 150 0 . , or =− 333 . Putting this into the equation (1) above gives −− = .. or v p 0346 . m s Then v g = 3 33 0 346 115 . af ms FIG. P9.21 *P9.22 For the car-truck-driver-driver system, momentum is conserved: ppp p 121 2 ii f f += + : 4 000 8 800 8 4 800 kg m s kg m s kg b g bg b g ej ±± ± ii i +− = v f v f = = 25 600 4800 533 kg m s kg . For the driver of the truck, the impulse-momentum theorem is Fp p t fi : Fi i 0120 80 8 s kg m s kg m s b g b g 178 10 3 . ± N on the truck driver For the driver of the car, i 8 s kg m s kg m s b g 889 10
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