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:

  1. Final momentum of object $=\frac{\text { Power } \times \text { time }}{\text { Speed of light }}$

$$ \begin{aligned} & =\frac{30 \times 10^{-3} \times 100 \times 10^{-9}}{3 \times 10^{8}} \\ & =1.0 \times 10^{-17} kg-m / s \end{aligned} $$



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