Two spacemen are floating together with zero speed in a gravity-free region of s

Question

Two spacemen are floating together with zero speed in a gravity-free region of space. The mass of spaceman A is 120 kg and that of spaceman B is 90 kg. Spaceman A pushes B away from him with B attaining a final speed of 0.5 m/s. The final recoil speed of A is: zero 0.38 m/s 0.5 m/s 0.67 m/s 1.0 m/s A uniform plank XY is supported by two equal 120-N forces at X and Y, as shown. The support at X is then moved to Z (half-way to the plank center). The supporting forces at Y and Z are then: Fy= 240 N, Fz = 120 N Fy = 200 N, Fz = 40N Fy= 40 N, Fz= 200 N FY= 80 N, Fz= 160 N FY= 160 N, Fz = 80 N

Explanation / Answer

(3)Mass of a space man A = Ma = 120kg Mass of the space man B = Mb 90kg since ,they coming from gravity free region of space their intial momemtum's are 0 thus, Acc. to consrevation of linaer momentum we have , 0 = Ma Va + MbVb 0 = 120(Va) + (90)(0.5) Va = - 0.375 or 0.38 m/s (appx.) (5)If z is excatly at center of the plank weights are eqully share on the X, Y ends but , If Z is moved Half way to tha plank (as in fig) now in this case weight will share as 2 : 1 thus, FY = 80 N , FZ = 160 N

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