A charged particle `(q,m)` is moving directly towards fixed positive charge `Q`. When it is at distance `d` from `Q`, it has speed `v_(0)`. At what distance `Q` will be particle come momentarily to rest ? Is the acceleration constant during motion ?

Explanation

Applying energy conservation between `①` and `②`
`K_(1) + U_(1) = K_(2) + U_(2)`
`(1)/(2) mv_(0)^(2) + (1)/(4 pi in_(0)) .(Qq)/(d) = 0 + (1)/( 4pi in_(0)) (Qq)/(r )`
`(1)/(r ) = (1)/(d) + (2 pi in_(0) mv_(0)^(2))/(Qq)`
Here , separation between charges is changing , `F prop (1)/(r^(2))`.