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Sahay Sir > Question Answers > Uncategorised (JEE Advanced Physics by BM Sharma + GMP Solutions) > An 80 kg boy and his 40 kg sister, both wearing roller blades, face each other at rest. The girl pushes the boy hard, sending him backward with velocity 3.0 m/s towards the west. Ignore friction, (a) Describe the subsequent motion of the girl. (b) How much chemical energy is converted into mechanical energy in the girl’s muscles? (c) Is the momentum of the boy-girl system conserved in the pushing apart process? How can it he with no motion beforehand and plenty of motion afterward?

An 80 kg boy and his 40 kg sister, both wearing roller blades, face each other at rest. The girl pushes the boy hard, sending him backward with velocity 3.0 m/s towards the west. Ignore friction, (a) Describe the subsequent motion of the girl. (b) How much chemical energy is converted into mechanical energy in the girl’s muscles? (c) Is the momentum of the boy-girl system conserved in the pushing apart process? How can it he with no motion beforehand and plenty of motion afterward?

An 80 kg boy and his 40 kg sister both wearing roller blades face each other at rest. The girl pushes the boy hard In figure a man stands on a boat floating in still water. The mass of the man and the boat is 60 kg and 120 kg respectively. a. If the man walks to the front of the boat and stops. what is the separation between the boat and the pier now? b. If the man moves at a constant speed of 3m/s relative to the boat sending him backward with velocity 3.0 m/s towards the west. Ignore friction what is the total kinetic energy of the system (boat + man)? Compare this energy with the kinetic energy of the system if the boat was tied to the pier.