Consider a spongy block of mass $m$ floating on a flowing river. The maximum mass of the block is related to the speed of the river flow $v$, acceleration due to gravity $g$ and the density of the block $\rho$ such that $m_{\text{max}} = k v^x g^y \rho^z$ ($k$ is constant). The values of $x$, $y$ and $z$ should then respectively be: