The frictional force acting on the block is given by $f_k = \mu_k N = \mu_k mg$, where $\mu_k$ is the coefficient of kinetic friction, $m$ is the mass, and $g$ is the acceleration due to gravity . Given values: $m = 50 \text{ kg}$, $\mu = 0.2$, and displacement $s = 1 \text{ m}$. Taking $g = 9.8 \text{ m/s}^2$: $f_k = 0.2 \times 50 \times 9.8 = 98 \text{ N}$. The work done against friction is the energy spent to overcome this opposing force over the given distance : $W = f_k \times s$ $W = 98 \text{ N} \times 1 \text{ m} = 98 \text{ J}$.