The force exerted is:\[ F = \frac{\Delta P}{\Delta t}. \]Here:\[ \Delta P = m \cdot v - 0 = 150 \times 10^{-3} \cdot 20 \, \text{kg m/s}, \]\[ F = \frac{150 \times 10^{-3} \cdot 20}{0.1}. \]\[ F = 30 \, \text{N}. \]Final Answer: 30 N.