Answer
The correct option is f. $30$kg m/s
Work Step by Step
The cart of mass $m = 10$kg shown in the image initially moves in the $-x$ direction(left) with a speed $2$ m/s. Thus its velocity is $v_i=-2$m/s. Its momentum is thus initially $p_i = m\times v_i = -20 $ kg m/s.
In the second case, the cart now has a speed $1$ m/s in the $+x$ direction(right) and hence has a velocity $v_f = 1$ m/s. Its momentum is now $p_f = m\times v_f = 10$ kg m/s.
The change in momentum is now given by
$\Delta p = p_f-p_i = 10 -(-20) = 30$kg m/s.
