Step 1: Understand the problem.
The power required to keep the conveyor belt moving is related to the rate of change of kinetic energy of the sand. The kinetic energy per unit time (power) is given by the formula:
\[
P = \frac{d}{dt} \left( \frac{1}{2} m v^2 \right)
\]
where \( m = 1.5 \, \text{kg/s} \) is the mass flow rate of sand, and \( v = 7 \, \text{m/s} \) is the velocity of the conveyor belt.
Step 2: Apply the formula.
The power required is:
\[
P = \frac{1}{2} \times 1.5 \times 7^2 = \frac{1}{2} \times 1.5 \times 49 = 36.75 \, \text{Watts}
\]
Step 3: Conclusion.
Thus, the power required to keep the conveyor belt running is 36.75 Watts.