A particle of mass $m$ falls from rest at $t=0$ from a height $h$ above ground level, assumed to be at $z=0$, subject to its weight and a linear drag force (air resistance) $F = -mfv$ proportional to its velocity, where $f > 0$.
Write down the equation of motion. Find the velocity and position as functions of time.
Write down the equation that determines the time $t_1$ at which the particle reaches ground level.
Any help? Thanks.