For a spring system designed to absorb energy, which of the following changes would most effectively increase the energy absorption capacity without altering the spring's stiffness (k)? 

Concept:

The energy absorbed by a spring is given by the formula:

\(U = \frac{1}{2} k x^2\)

Where, U is the energy stored, k is the stiffness of the spring, and x is the deflection from its natural (free) length.

Calculation:

To increase the energy absorption capacity without changing the stiffness k, we need to increase the value of x, i.e., the maximum allowable deflection of the spring.

By increasing the spring's free length, the spring can be deflected more before reaching its solid height (fully compressed condition), allowing more energy to be absorbed.