A boy of mass 60 kg is standing over a platform of a mass 40 kg placed over a smooth horizontal surface he throws a stone of mass 1 kg velocity v is equal to 10 m s to the power minus 1 at an angle of 45 degree with respect to the ground the displacement of a platform with boy on the horizontal surface when the stone lands on the groand is

Please explain the meaning of question

total mass of body and plateform = 100kg

 conservation of momentum in horizontal direction     100V + 1*10cos45 =0

                                                                               V=-1/10√2 m/sec 

 negative sign indicates in the reverse direction.

 time  of filght = 2*10 sin 45 /10

                    = √2

 so in this time plateform will move  = V*t

                                                    = 1/10√2 * √2

                                                    = .1 m = 10 cm Answer