The current is zero in a conductor when no potential difference is applied because: a) the electrons are not moving b) the electrons are not moving fast enough c) for every electron with a given velocity there is another with a velocity of equal magnitude and opposite direction d) equal numbers of electrons and protons are moving together e) otherwise ohm's law would not be valid

C) for every electron with a given velocity there is another with a velocity of equal magnitude and opposite direction

Explanation:

Each electron has an equal and opposite speed to that of another electron. Therefore, there will be no net flow of charges in one direction and the current is zero. By applying a potential difference, the net flow of electrons has a predominant direction towards the positive end of the electric field.

in physics zero. in muscle fatigue could be high

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.