That's general kinematics. You can't just plug in the exact numbers for the exact equations and hope for the best. At what rate is David accelerating when he jumps off? I assume that his initial vertical v is zero. If you figure that out, you can find the unknown y.
Off the top of my mind, I think her equations are supposed to be general. You can substitute delta y for delta x. If you continue on with that assumption, does it get you the right answer?
Homework Statement
Given a wire with length a and square base b x b (where a >> b), show that the first 1700 (approximately) levels of the electron in the wire are identical for the one dimensional box, when a = 1m and b = 1mm.
Homework Equations
I know that the allowed energies of...