A sled with mass 7.80 moves in a straight line on a frictionless horizontal surface. At one point in its path, its speed is 4.00 ; after it has traveled a distance 2.50 beyond this point, its speed is 6.10 .
A) Use the work-energy theorem to find the force acting on the sled, assuming that this force is constant and that it acts in the direction of the sled's motion.