##m=.3 kg, v = 11 \frac {m}{s}, t = .25 s, \vec v_1 = mv\langle cos(-55), sin(-55) \rangle, \vec v_2 = mv\langle cos(25), sin(25) \rangle##
$$m\vec v_1 - m\vec v_2 = \vec Ft = mv\langle cos(25)-cos(-55), sin(25)-sin(-55) \rangle$$
$$Ft = mv\sqrt{(cos(25)-cos(-55))^2 + (sin(25)-sin(-55))^2}$$
$$F...