Answer
The car exerts a force of 1200 N on the trailer.
Work Step by Step
Let's find the acceleration of the car-trailer system.
$\sum ~F = ma$
$F - F_f = ma$
$a = \frac{F-F_f}{m} = \frac{(3.6 \times 10^3 ~N)-(350 ~kg)(9.80 ~m/s^2)(0.15)}{1280 ~kg + 350 ~kg}$
$a = 1.9 ~m/s^2$
Let's consider the force equation on the trailer.
$\sum F = ma$
$F - F_f = ma$
$F = F_f + ma$
$F = (350 ~kg)(9.80 ~m/s^2)(0.15) + (350 ~kg)(1.9 ~m/s^2)$
$F = 1200 ~N$
The car exerts a force of 1200 N on the trailer.