I sent a question a few minutes ago and received an answer. However, because I cannot respond back on the same post, I am putting the answer here since I still need a bit of help :)
The spring scale reads the measures in Newtons, so I know I can find the force with that. However, I am not sure how to do the procedure experimentally more specifically. I was thinking I could pull the person in the cart with a constant force for a certain distance and a certain amount of time to find it's constant velocity. Then I could release the person and measure the distance and time taken to stop, so the constant velocity calculated earlier would be my Vinitial and Vfinal=0. Finally, with that data, I could manipulate the equations to find the unknown. Does that sound right?
Also, would the acceleration calculated from the kinematic equations be same one that is used in F=ma and the force with which I pulled the person is F. So the only thing missing would be m, right?