A \(400-\mathrm{kg}\) shipboard cannon fires a \(20-\mathrm{kg}\) ball at \(60 \mathrm{~m} / \mathrm{s}\). The cannon's resulting recoil speed across the deck is regarded as excessive. How much inertia (in the form of sandbags, say) must be added to the cannon if its recoil speed must be reduced to \(2.0 \mathrm{~m} / \mathrm{s}\) ?