physics---mechanics

(a) Net force = (1200 - 400 -200) N = 600 N
Hence, acceleration = 600/(800+200) m/s2 = 0.6 m/s2
(b) Let T be the tension in the towbar, use net-force = mass x accelerationT - 200 = 200 x 0.6

T = 320 N

(c) Let a be the decceleration of the car and trailerConsider the trailer,100 + 200 = 200a
i.e. a = 300/200 m/s2 = 3/2 m/s2

Consider the car,
(F + 400) - 100 = 800 x (3/2)
hence F = 900 N