A sled initially at rest on a frictionless, horizontal stretch of ice is pulled by a constant horizontal force of 50N over a distance of 40m. As it leaves the force region, the sled's speed is measured to be 8.0m/s. Which of the following values is closest to the mass of the sled?
a) 32 kg
b) 63 kg
c) 125 kg
d) 16 kg