A boy throws a 4kg pumpkin at 8m/s to a 40kg girl on roller skates, who catches it. At what speed does . . .?

the girl the move backward?

A boy throws a 4kg pumpkin at 8m/s to a 40kg girl on roller skates, who catches it. At what speed does . . .?
who knows? We don't even know that the girl was stationary, that the trajectory vector was directly backward relative to the girl or that the girl caught the pumpkin so that there was zero angular momentum imparted...
Reply:Are these magic zero-friction rollerskates?
Reply:assuming the girl is stationary when she catches the pumpkin, as well as no drag or gravity losses in the pumpkin during transfer:





this is strictly a conservation of momentum problem:





m1*v1 = m2 * v2





object 1=pumpkin


object 2=girl + pumpkin





so that means that m1=4kg and m2=(4+40)=44kg and v1=8m/s





so now left with one unknown variable; solve:





v2= (m1*v1)/m2 = (4kg * 8m/s)/44kg





v2 = 8/11 m/s or in decimal form v2 = .727 m/s





the girl is moving backwards but still in the direction that the pumpkin was thrown to her, so no negative sign is there.





hope that helps



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