Please explain how the r.h.s of equation in box comes?

Physics (Mechanics) Example : A body of mass 'm' falls from rest at a height h under gravity (acceleration due to g) through a dense medium which produces resistive force F = -kv, where k is a conserve and 'v is the speed. It will hit the ground with a kinetic energy ? Solution: F = ma, TIPS Drag Force Always Applied opposite to the velocity. mg kv2 = maa (6) in Terms of Position (x) X = 0Qu = 0 dv mg- kV2 = mv- dx h F=-kv dv kv2 dx9 +X m mg vdv = dx x = h g-V m Integrating both sides vdv - - fdx og-2 m k g 2=t m Let 2y dv dt m m vdv -dt 2k m dt = X 2k t 2kx log, (t) = m g- m log om 2kx m g 2kx kv2 e m