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ICSE Class 10 Physics 2014 Paper

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Question : 48 of 66
Marks: +1, -0
A radar sends a signal to an aircraft at a distance of 30 km30\ \mathrm{km} away and receives it back after 2×10−42 \times 10^{-4} second. What is the speed of the signal ?
Solution:  
Given :
Distance of aircraft =30 km=30,000 m=30\ \mathrm{km}=30,000\ \mathrm{m}
Total distance =2×30,000=60,000 m=2 \times 30,000=60,000\ \mathrm{m}
Time taken =2×10−4=2 \times 10^{-4} second
Hence Speed of signal (V)
  =    Total distance travelled  (2d)  time taken  (t)\;=\;\frac{\;\text{Total distance travelled}\;(2d)}{\;\text{time taken}\;(t)}
  =  60,0002×10−4=30,000×104 m/s\;=\;\frac{60,000}{2 \times 10^{-4}}=30,000 \times 10^4\ \mathrm{m}/\mathrm{s}
  =3×108 m/s\;=3 \times 10^8\ \mathrm{m}/\mathrm{s}
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