2 positively charged particle X and Y are initially far away from each other and at rest.X begins to move towards Y with some initial velocity. The total momentum and energy of the system are p and E.

A)   If Y is fixed, both p and E are conserved.

B)  if Y is fixed E is conserved but not p.

c)  if both are free to move, p is conserved but not E.

d)  if both are free, E is conserved but not P.

plz do reply and post ur attempt. i know the answer to this one but can't understand it. ( rates for correct answer+explanation)

 i think ans is B

momentum wud not be conserved b;coz an external force wud then be required to keep Y as fixed

and as we knw when an net xternal force is acting momentum is not conserved

E is conserved b'coz the work done by the force is 0 as the Y particle is not moving on which the xternal force is acting

yarro E toh conserve ho ga hi..

mom isnt conserved becoz to make y fixed we have to apply force..and mom. isnt conserved in that dir where external force is non zero..

if y is free then both E and P is conserved ..

so the ans. must be B.

If we consider B) then E is conserved but not the momentum of the system as external force needs to be acted upon the system.