"A 93kg water skier floating in a lake is pulled from rest to a speed of 13 m/s in a distance of 20m. What is the net force exerted on the skier, assuming his velocity is constant. So I know I have to find the force I'm going to need acceleration, and to find it I'll need to use a kinematic equation. So this is where the confusion comes in. The correct way to do it is v^2= U^2 + 2ad, and isolate the a. The answer to this would be 4.22 m/s^2. Then we can find the force by plugging it in, f=(4.22)(93)= 392 Newtons But why couldn't I use this kinematic equation and solve for a? x=x0 + v0t + 1/2(a)t^2) 20=0+0+1/2(a)(16) 20=8a 20/8 = a Sorry if this seems like a dumb question but I think all the different letters and their meanings are getting a little confusing. Or this one, acceleration = delta V / Delta T, couldn't you just do 13-0 / 4-0? so its 13/4?