A 61.0 kg boy and his 42.0 kg sister, both wearing roller blades face each other

Question

A 61.0 kg boy and his 42.0 kg sister, both wearing roller blades face each other at rest. The girl pushes the boy hard, sending him backward with a velocity 3.00 m/s toward the west. Ignore friction. a) Describe the subsequent motion of the girl. This answer has not been graded yet. (b) How much chemical energy is converted into mechanical energy in the girl's muscles? J (c) Is the momentum of the boy-girl system conserved in the pushing-apart process? How can it be, with large forces acting? How can it be, with no motion beforehand and plenty of motion afterward? This answer has not been graded yet.

Explanation / Answer

1.The girl will go in uniform motion subsequently as there is no friction.

3.The momentum of girl boy system will be conserved because there is no external force acting on the system

2.Conservation of momentum : 0=-42*3+61*v

=> v=2.06 m/s

Energy given to boy =0.5*42*(2.06)^2 =89 J =Energy required

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