The force $\mathbf{F},$ acting in a constant direction on the $20-\mathrm{kg}$ block, has a magnitude which varies with the position $s$ of the block. Determine how far the block must slide before its velocity becomes $15 \mathrm{m} / \mathrm{s}$. When $s=0$ the block is moving to the right at $v=6 \mathrm{m} / \mathrm{s}$. The coefficient of kinetic friction between the block and surface is $\mu_{k}=0.3.$