For q1), when you do the calculation, you should get positive or negative velocities which give you the direction. So just assume one of the particles moves in a positive direction at the start of the question. Have a think about whether it matters which one you choose. The question seems to be deliberately vague in this respect to check whether you understand how to do it, so you'll need to practice / get used to it.
For q9), the truck is brakeing, which direction is the force acting on the truck? What will happen to the car, which direction will the force be acting through the towbar? Just think about whether the vehicles will have a positive or negative acceleration, the direction should be obvious. The towbar is rigid, so it directly transmits the force, you don't have to try and give it another name.