A particle of mass 2g & charge 1coulomb is held at rest ona frictionless horizontal surface at a distance of 1 m from fixed charge 1mC. If the particle is released it will be repelled .The speed of the particle when it is at a distance of 10m from fixed charge is??In the solution of this question , mechanical energy is conserved but how??? and why momentum cant be conserved in this ques.?? plzz explain..

Coulombic forces are conservative forces hence the mechanical energy can be conserved because no energy is extracted from the system.The total momentum is not conserved because while fixing the charge at its position ull have to apply a force.

the solution which i think u must have figured out is 90000 m/sec

Approved

Dear Ranjita yadav,

Since no energy is extracted from the system,mechanical energy is conserved .

By applying a force the charge is fixed to its position and because of this the total momentum of the system is not conserved ..

All the Very Best & Good Luck to you ..

Hope this helped you immensely...

Regards,

AskIITians Expert

Godfrey Classic Prince

IIT-M

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How no energy is extracted??? if we apply force to fix charge..how does it affect the momentum ..plzz explain..!!

try thinking in this way there is no friction nor any resistive force acting on the charge hence the system only transits from potential energy to kinetic energy no other energy transformation occurs.

conservation of momentum is valid when no EXTERNAL force acts, but to hold the 1 mC charge in place u have to apply some force other wise it will move under the repulsion from the 1C charge.(the forces between the charges are internal and cancel out in pairs)