2016 · Q49
A person rings a metallic bell near a strong concrete wall. He hears the echo after 0.3 s. If the sound moves with a speed of 340 m/s, how far is the wall from him?
General KnowledgePhysics
- A102 m
- B11 m
- C51 m
- D30 m
Explanation
The echo travels from the person to the wall and back, so the total distance covered is twice the distance to the wall: 2d = v x t. With v = 340 m/s and t = 0.3 s, 2d = 340 x 0.3 = 102 m, giving d = 51 m. Option (A) forgets to halve the round-trip distance, while (B) and (D) do not follow from the calculation. The wall is 51 m away, option (C).