The pieces will fly off in opposite directions to conserve momentum so:
m₁v₁ = m₂v₂
m₁v₁ = 1.6m₁v₂
v₂ = v₁/1.6
Ratios of K.E = m₁(v₁)²/m₂(v₂)²
= m₁(v₁)² / 1.6m₁(v₁/1.6)²
= 1.6
K.E₁ = 1.6K.E₂
5900 = K.E₁ + K.E₂
5900 = 1.6K.E₂ + K.E₂
K.E₂ = 2270 J for larger piece
K.E₁ = 3200 J for smaller piece