Answer
Since the object started from rest, the change in momentum is $100~kg~m/s$
Work Step by Step
We can find the speed after it falls for $3.4~s$:
$v_f = v_0+at = 0+(9.80~m/s^2)(3.4~s) = 33.32~m/s$
We can find the momentum:
$p = mv = (3.0~kg)(33.32~m/s) = 100~kg~m/s$
Since the object started from rest, the change in momentum is $100~kg~m/s$.
