problem solving in 2nd law of motion?

Answer 1

The most accurate statement of Newton's second law of motion is F = dp/dt, i.e., "Force is equal to the time rate of change of momentum." However, when the velocities involved are much smaller than the speed of light, we use the formula F = ma ("Force is equal to the product of mass and acceleration.") because we can assume constant mass, an assumption that is not valid at higher velocities.

You would typically be given enough information to calculate two of the values, and asked to solve for the third, which can be done algebraically. For example, you might have to sum multiple forces to find the resultant force, and then divide a change in velocity by time to get acceleration, and then divide force by acceleration to get mass.