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ICSE Class 10 Physics 2017 Paper

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Question : 14 of 65
Marks: +1, -0
An enemy plane is at a distance of 300 km300\ \mathrm{km} from a radar. In how much time the radar will be able to detect the plane? Take velocity of radiowaves at 3×108 ms−13 \times 10^8\ \mathrm{ms}^{-1}.
Solution:  
Given : d=300 km=300×103 m, V=3×108d=300\ \mathrm{km}=300 \times 10^3\ \mathrm{m},\ V=3 \times 10^8  ms−1\ \mathrm{ms}^{-1}.
We know, V  =  2dtV\;=\;\frac{2d}{t}
∴ t  =  2dv  =  2×300×1033×108\therefore\ t\;=\;\frac{2d}{v}\;=\;\frac{2 \times 300 \times 10^3}{3 \times 10^8}
  =2×10−3 sec.\;=2 \times 10^{-3}\ \mathrm{sec}.
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