Question

An echo is heard by a radar in $0.08\mathrm{s}$. If velocity of radio waves is $3\times {10}^8{\mathrm{ms}}^{-1}$, how far is the enemy plane?

Answer 1

Step 1: Given data:
Time,$t=0.08\mathrm{s}$
Velocity,$\mathrm{v}=3\times {10}^8{\mathrm{ms}}^{-1}$
Step 2: Formula used
Speed of sound, $S=\frac{\mathrm{Distance}}{\text{Time}}$

$dis\tan ce=speed\times time$

Step 3: Find the distance

An echo is heard when the sound travels from the source to the barrier which reflects the sound and the sound travels back to the source.
Thus, the distance covered in $0.08s$ is $2\times dis\tan ce$

Distance of the enemy plane person from the cliff
$2\times dis\tan ce=speed\times time$

so,$dis\tan ce=\frac{speed\times time}{2}$

$=\frac{3\times {10}^8\times 0.08}{2}$

$=\frac{3\times {10}^8}{2}\times \frac{8}{100}$

$=12000000\mathrm{m}$

$=\frac{12000000}{1000}$

$=12000km$

Thus, the distance of the enemy plane from the cliff from which the echo is heard is $12000km$.