A porter lifts a heavy suitcase of mass 80 kg and at the destination lowers it down by a distance of 80 cm with a constant velocity. Calculate the work done by the porter in lowering the suitcase. (take $$g = 9.8$$ ms$$^{-2}$$)

The porter lowers the suitcase with constant velocity, meaning the net force is zero. We need to find the work done by the porter (i.e., the work done by the force applied by the porter).

The suitcase has mass $$m = 80 \text{ kg}$$ and is lowered by a distance $$d = 80 \text{ cm} = 0.80 \text{ m}$$.

Since the suitcase moves down with constant velocity, the porter applies an upward force equal in magnitude to the weight: $$F_{\text{porter}} = mg = 80 \times 9.8 = 784 \text{ N (upward)}$$

The displacement is downward ($$d = 0.80 \text{ m}$$ downward), while the force is upward. Since force and displacement are in opposite directions, the work done by the porter is negative: $$W_{\text{porter}} = -F \cdot d = -(784)(0.80) = -627.2 \text{ J}$$

The work done by the porter in lowering the suitcase is $$-627.2 \text{ J}$$.