Using the work-energy theorem, the total work done on the block as it slides to rest is the negative work performed by friction. If the average magnitude of friction is [tex]F[/tex], then
[tex]W_{\rm total} = \Delta K \\\\ \implies -F(1.7\,\mathrm m) = 0 - \dfrac12(15\,\mathrm{kg})\left(0.5\dfrac{\rm m}{\rm s}\right)^2 \\\\ \implies F = 1.875\,\mathrm N \approx \boxed{1.9\,\mathrm N}[/tex]
