A rifle fires a 1.06 x 10-2-kg pellet straight upward, because the pellet rests on a compressed spring that is released when the trigger is pulled. The spring has a negligible mass and is compressed by 6.61 x 10-2 m from its unstrained length. The pellet rises to a maximum height of 6.26 m above its position on the compressed spring. Ignoring air resistance, determine the spring constant.

 k = 2.65 10² N / m

Explanation:

As the pellets shoot up we can use energy conservation

Starting point. Compressed spring rifle

            Em₀ = Ke = ½ k x²

Final point. Highest point of the path

            = U = m g y

Energy is conserved

            Em₀ = Em_{f}

           ½ k x² = m g y

           k = 2 m g y / x²

Let's calculate

            k = 2  1.06 10⁻²  9.8  6.26 / (6.61 10⁻²)²

             k = 2.65 10² N / m

true tan speed = ang vel x radius

it would be kevlar ^^