Solve the following :


Raindrops of radius $1 \mathrm{~mm}$ and mass $4 \mathrm{mg}$ are falling with a speed of $30 \mathrm{~m} / \mathrm{s}$ on the head of a bald person. The drops splash on the head and come to rest. Assuming equivalently that the drops cover a distance equal to their radii on the head, estimate the force exerted by each drop on the head.


From $^{v^{2}}=u^{2}-2 a s$

$a=\frac{v^{2}-u^{2}}{2 s}=\frac{-(30)^{2}}{2 \times 10^{-3}}=-4.5 \times 10^{5} \mathrm{~m} / \mathrm{s}^{2}$

$F=m a=4 \times 10^{-6} \times 4.5 \times 10^{5}=1.8 \mathrm{~N}$


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