How to design a shock uv absorber

We consider an elastic bar of length ℓ, subject to the longitudinal impact of a mass hitting one end of it, while the other end is fixed. If the cross-section of the bar is constant, it is known how to determine the influence of the inertia of the bar on the velocity of the impinging mass and on the maximal compression of the bar. If, however, the cross-section can vary, preserving the total volume of material, the question arises of distributing this material along the span of the bar so as to minimize the maximal compression.How to design a shock uv absorber