bi) resultant force A is the sum of forces at the four contact points of the car.Resultant force C is the sum of forces from all the components of the car.
biii) friction oppose motion is incorrect here.Need to elaborate: The contact force between the car and the road is at an angle . The component along the surface is friction. The friction is opposite to the direction of motion but produces a forward force on the car in the direction of motion. Note the direction.
Another example: When we walk , our feet and the floor produces friction that can propel us forward or stop. The trailing feet gives us frictional force foward and the front feet gives us the frictional force backwards to enable us to stop. We manipulate direction of friction to enable us to accelerate and decelerate when we are walking.
c) It is pointless to say 'ice skating' or 'being is space' as your answer eventhough these are places where there in no friction. The question want you to give a situation where motion is produced without friction. The answer is just : If an object were to fall , motion is produced by lost of PE.
