Which of the following is a noncontact force? a. electrical forces b. gravitational forces c. magnetic forces d. all of these

D. all of these

Explanation:

Electric forces, gravitational forces and magnetic forces are non contact forces. These forces are also the fundamental forces. Non contact forces are the forces which applied on a body without any real touch. Generally these non contact forces are in equilibrium.

we need to know the time interval during which the force acts. impulse of force = momentum change

the minimum amperage that the current in this wire would have to have so that its weight is completely supported by the magnetic force due to earth's field, assuming that no other forces except gravity act on it