A pulse of light of duration 100 ns is absorbed completely by a small object initially at rest. Power of the pulse is 30 mW and the speed of light is . The final momentum of the object is [2013]

Question

A pulse of light of duration 100 ns is absorbed completely by a small object initially at rest. Power of the pulse is 30 mW and the speed of light is $3 \times 10^{8} {ms}^{- 1}$ . The final momentum of the object is [2013]

Smart Achievers · Accepted Answer

(3)

Final momentum,

$p = \frac{E}{c} = \frac{P \times t}{c} = \frac{30 \times 10^{- 3} \times 100 \times 10^{- 9}}{3 \times 10^{8}}$

$= 1.0 \times 10^{- 17} kg {ms}^{- 1}$

Solution

Q.
A pulse of light of duration 100 ns is absorbed completely by a small object initially at rest. Power of the pulse is 30 mW and the speed of light is $3 \times 10^{8} {ms}^{- 1}$ . The final momentum of the object is [2013]

1 $0.3 \times 10^{- 17} kg {ms}^{- 1}$

2 $3.0 \times 10^{- 17} kg {ms}^{- 1}$

3 $1.0 \times 10^{- 17} kg {ms}^{- 1}$

4 $9.0 \times 10^{- 17} kg {ms}^{- 1}$

Ans.
(3)

Final momentum,

$p = \frac{E}{c} = \frac{P \times t}{c} = \frac{30 \times 10^{- 3} \times 100 \times 10^{- 9}}{3 \times 10^{8}}$

$= 1.0 \times 10^{- 17} kg {ms}^{- 1}$

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Solution

Q. A pulse of light of duration 100 ns is absorbed completely by a small object initially at rest. Power of the pulse is 30 mW and the speed of light is 3×108 ms-1. The final momentum of the object is [2013]

1 0.3×10-17 kg ms-1

2 3.0×10-17 kg ms-1

3 1.0×10-17 kg ms-1

4 9.0×10-17 kg ms-1

Ans. (3) Final momentum, p=Ec=P×tc=30×10-3×100×10-93×108 =1.0×10-17 kg ms-1