The pattern will be at the same place at 2 feet, 4 feet, 6 feet, 8 feet, 10 feet, 12 feet, 14 feet, 16 feet, and 18 feet
When you make the product of a binomial of the kind x + a times other binomial that is of the kind x - a, you obtain another binomial (not a trinomial), so any example with that form will be a counterexample that disproves the conjecture:
(x + a) * (x - a) = x^2 - a^2
For example, (x +3) * (x - 3) = x^2 - 9. So, not always the product of two binomials is a trinomial.
In a mechanical system, it is a law that energy should be conserved. In this case, what is the initial energy should be equal to the total energy after the motion happened. We do as follows:
PE(at rest) = KE(during motion) + PE(after motion)
51450 J = KE(during motion) + 32781 J
KE(during motion) = 18669 J