how about projectile motion? and a swimmer question with current?
okay break it down into components. pretty much find the angle the swimmer is going and the opposite always use Sin for the X and Cos for the Y direction component. once you get the answer use pythagorean theorem and use inverse tan and divide it by the Dt(total displacement) and you should get whatever you are finding.
depends what you are given. Isolate for average velocity the equation be v = d/t if its constant velocity if not use one of the kinematic equations. same for time. and for net force it can easily depend. is it force of friction or tension you are looking for? you must always divide by the mass according to Newton's second law.