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.
Let \( T_r \) be the \( r^{\text{th}} \) term of an A.P. If for some \( m \), \( T_m = \dfrac{1}{25} \), \( T_{25} = \dfrac{1}{20} \), and \( \displaystyle\sum_{r=1}^{25} T_r = 13 \), then \( 5m \displaystyle\sum_{r=m}^{2m} T_r \) is equal to: