Please explain ex. dm kt, where m is the by dt dv dm dt = mg motion of the rain drop is m dm dt t0. with zero initial velocity and initial mass m, (m, = 2 gm, k

please explain Ex. dm kt, where m is the by dt dv dm dt = mg motion of the rain drop is m dm dt t0. with zero initial velocity and initial mass m, (m, = 2 gm, k = 12gm/ If the drop starts s and g= 1000 cm/s*), the velocity v of the drop after one second is IT-JAM 2011 (A) 250 cm/s (B) 500 cm/s (C) 750 cm/s (D) 1000 cm/ls