A dog barks in a park and hear its echo after 0.5 seconds. The sound of its bark got reflected by a nearby building. The sound of speed in air is 346 m/s. The distance between the dog and the building isA) 86.5 mB) 80.6 mC) 75 mD) 8.65 m

When the dog barks, the sound covers the distance x and gets reflected back from the building after covering distance x once again so that echo is heard.

So, the sound covers 2x distance in 0.5 s.

Therefore,

$\mathrm{Distance}=\mathrm{time}\times \mathrm{velocity}\phantom{\rule{0ex}{0ex}}\Rightarrow 2x=0.5\times 346\phantom{\rule{0ex}{0ex}}\Rightarrow x=\frac{0.5\times 346}{2}=86.5\mathrm{m}$

Therefore, the correct option is A.

**
**