What approximations or simplifying assumptions did you have to make in your analysis which might not be adequately valid? (Don't check any approximations or simplifying assumptions which in fact have negligible effects on your numerical results.)

a. Neglect air resistance, despite fairly high speeds.
b. Assume tension in cord proportional to stretch, even for the very large stretch occurring here.
c. Assume the speeds are very small compared to the speed of light.
d. Assume that the gravitational force hardly changes from the top of the jump to the bottom.