Answer
The correct answer is (b) 0.075 g.
Work Step by Step
We can use conservation of momentum to solve this question. Let $w$ be the water drop and let $i$ be the insect.
$(m_i+m_w)~v_i = m_w~v_w$
$m_i = \frac{m_w~v_w - m_w~v_i}{v_i}$
$m_i = \frac{(3\times 10^{-4}~kg)(2.5~m/s) - (3\times 10^{-4}~kg)(2.0~m/s)}{2.0~m/s}$
$m_i = 7.5\times 10^{-5}~kg = 0.075~g$
The correct answer is (b) 0.075 g.
