Frictional force on the front wheel of a rear wheel drive car 
In the above problem, it is stated that the front wheels are "free to roll". The solution to this problem doesn't take into account the friction acting on the front wheels in the free body diagram it presents.
I would think that, even though the wheels are "free to roll", there would still have to be a static frictional force acting to the left to cause its angular acceleration. Is ignoring this force just to simplify the problem, or am I misunderstanding something?
 A: I add an edit, since it is too long for a comment.
It does not seem so easy to apply Coulomb's law for friction because when the truck accelerates, it tends to turn on itself which increase the normal reactions on the rear wheels (with respect to static situation). That's why powerful cars often have rear-wheel drive.
The angular momentum theorem has to be applied to the whole truck to find the normal reactions on the rear wheels. And it does  depend on the position of the center of gravity of the truck.
If the inertia of the front wheels is neglected, the tangential force required to made them turn is zero. (To see this, it suffices to apply the angular momentum theorem at the center of gravity of the wheel).
Sorry for my poor english.
A: It says to ignore the mass of the wheels, meaning all 4. It also says the front wheels are free to roll, mraning to ignore friction. This is to simplify the problem. This is to teach the basics of acceleration problems. Once all variables are considered the problems become more difficult.
