Sand is falling on a conveyor belt at the rate of $5kg{s}^{-1}$. The extra power required to move the belt with a velocity of $6m{s}^{-1}$is,

$$\begin{gathered} Power =Force . velocity \\ \Rightarrow P=\frac{dp}{dt}.v here p= momentum=mass \left(velocity\right) \\ \Rightarrow P=v\frac{dm}{dt}.v \\ substitute given values \\ \Rightarrow P=6\left(5\right).\left(6\right) \\ \Rightarrow P=180 watt \end{gathered}$$