The rain drop of mass \( 1\,\text{g} \) starts with zero velocity from a height of \( 1 \,\text{km} \). It hits the ground with a speed of \( 5\,\text{m/s} \). The work done by the unknown resistive force is ______ \( \text{J} \). (Take \( g=10\,\text{m/s}^2 \))
