Solving Sets of Equations

Given:

• a set of equations

fall:

((= gravity '(q 9.80665 (/ m (* s s))))
 (= horizontal-velocity '(q 0 (/ m s)))    ; default
 (= height   (* 1/2 (* gravity (expt time 2))))
 (= velocity (* gravity time))             ; vertical
 (= kinetic-energy
    (* 1/2 (* mass (expt total-velocity 2))))
 (= horizontal-distance (* horizontal-velocity
                           time))
 (= total-velocity
    (sqrt (+ (expt velocity 2)
             (expt horizontal-velocity 2))))

• a set of variables with known values:
  ((TIME 4))

• a variable whose value is desired: HEIGHT