Energy, work and power — practice question

A block with mass $20\,\text{kg}$ is initially at rest at the top of a plane that slopes at $30^{\circ}$ to the horizontal. It is launched at speed $5\,\text{m s}^{-1}$ along a line of greatest slope down the plane. A resistance force acts on the block. When the block has travelled $2\,\text{m}$ down the plane from the point from which it was projected, the work done against the resistance force is $50\,\text{J}$.