Centre of Mass 4 Question 2
3. A pulse of light of duration $100 ns$ is absorbed completely by a small object initially at rest. Power of the pulse is $30 mV$ and the speed of light is $3 \times 10^{8} ms^{-1}$. The final momentum of the object is
(a) $0.3 \times 10^{-17} kg-ms^{-1}$
(b) $1.0 \times 10^{-17} kg-ms^{-1}$
(c) $3.0 \times 10^{-17} kg-ms^{-1}$
(d) $9.0 \times 10^{-17} kg-ms^{-1}$
(2013 Adv.)
Objective Questions II (One or more correct option)
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Answer:
Correct Answer: 3. (b)
Solution:
- Final momentum of object $=\frac{\text { Power } \times \text { time }}{\text { Speed of light }}$
$$ \begin{aligned} & =\frac{30 \times 10^{-3} \times 100 \times 10^{-9}}{3 \times 10^{8}} \\ & =1.0 \times 10^{-17} kg-m / s \end{aligned} $$
