Identical twins, each with mass 59.6 kg, are on ice skates and at rest on a frozen lake, which may be taken as frictionless. Twin A is carrying a backpack of mass 12.0 kg. She throws it horizontally at 3.00 m/s to Twin B. Neglecting any gravity effects, what are the subsequent speeds of Twin A and Twin B?

Question

Identical twins, each with mass 59.6 kg, are on ice skates and at rest on a frozen lake, which may be taken as frictionless. Twin A is carrying a backpack of mass 12.0 kg. She throws it horizontally at 3.00 m/s to Twin B. Neglecting any gravity effects, what are the subsequent speeds of Twin A and Twin B?
Twin A    	  m/s
Twin B    	  m/s

Steve · Accepted Answer

momentum of A and P (pack) is conserved, so

v*59.6 + 3*12 = 0
v = -.60 m/s for twin A

after catching the pack, momentum of P and B is conserved, so

3*12 = v(12+59.6)
v = .50 m/s for B+pack

-.6*59.6 + .5*71.6 =~ 0 as expected