'N' number of balls of mass ' $\mathrm{m}^{\prime} \mathrm{kg}$ moving along positive direction of…
'N' number of balls of mass ' $\mathrm{m}^{\prime} \mathrm{kg}$ moving along positive direction of $\mathrm{x}$ - axis, strike
a wall per second and return elastically. The velocity of each ball is 'u' $\mathrm{m} / \mathrm{s}$. The
force exerted on the wall by the balls in newton, is
$\mathrm{m} \mathrm{Nu}$
0
$2 \mathrm{mNu}$
$\frac{\mathrm{mNu}}{2}$
Solution
N number of balls of mass m kg moving along positive direction of X -axis, strike a wall per second and return elastically. The velocity of each ball is $u \mathrm{~m} / \mathrm{s}$. The force exerted on the wall by the balls in newton, is $\mathbf{2 m N u}$.
The change in momentum of one ball,
$\Delta \mathrm{p}=\mathrm{mu}-(\mathrm{mu})=2 \mathrm{mu}$
The force exerted on the wall by N balls,
$\begin{aligned}
& F=\frac{\text { Change in momentum for } \mathrm{N} \text { balls }}{\text { Total time }(\mathrm{t})} \\
& =\frac{2 \mathrm{~m} \mathrm{Nu}}{1} \quad \ldots .(\because \mathrm{t}=1 \mathrm{~s}) \\
& =2 \mathrm{~m} \mathrm{Nu}
\end{aligned}$