I think it's starting to come together now.

The recurring problems you have would be consistent with treating velocity and momentum as scalars. Maybe you don't realize they're vectors? F=ma and p=mv are actually a vector equations. They can give wrong results if you only put the magnitudes of the quantities into them.


Can an object accelerate if its speed remains constant?

If an object reverses direction, must its momentum change?

If an object reverses direction, must its velocity change?

If an object reverses direction, must its speed change?

Is it possible to apply an unbalanced force to a moving mass without changing its speed?