Vectors will not follow the rules of general algebra. To determine the magnitude of a vector quantity, you have to follow the rules of vector algebra. 1. Suppose you are sitting in a moving train with a velocity of 80 m/s. And another train is coming from the opposite direction with a real velocity of 60 m/s. But when you look at that train, the train goes out of your side at a very fast speed. And then when you are asked what was the velocity of your respect other train?

that would be because of both gravity and friction. so     c

force is based upon mass and acceleration.the statement is not always true.

it can be explained from newton's second law of motion.

as per newton's second law of motion the rate of change of momentum is directly proportional to the applied force and takes place along the direction of force.

mathematically it can be written as -

                                              ⇒      

here   k is the proportionality constant whose value is 1.

                                                            [a is the acceleration=dv/dt]

hence we see that force not only depends on mass and acceleration but also on velocity and rate of change of mass. force f will depend on mass and acceleration only when mass is constant.

hence the statement that force is based upon mass and acceleration is false.