國中教甄｜理化理化109 年第 83 題單選題

When a rocket is traveling toward a mountain at 100 m/s, the sound waves from this rocket's engine approach the mountain at speed of $V$ . If the rocket doubles its speed to 200 m/s, the sound waves from the engine will now approach the mountain at speed of \_\_\_\_.

A$4V$

B$2V$

C$\sqrt{2}V$

D$V$正確答案

答案與詳解

正確答案

聲波在空氣中的傳播速度由介質決定，與火箭（聲源）速度無關，所以仍為 V。

A$4V$✕ 錯誤

聲速不會因為聲源速度加倍而變成 4 倍；聲波傳播速度取決於介質性質，不是聲源速度。

B$2V$✕ 易錯陷阱

直覺上可能以為火箭速度加倍，聲波接近山的速度也加倍，但聲波一旦在空氣中傳播，其速度由空氣決定。

C$\sqrt{2}V$✕ 錯誤

D$V$✓ 正確

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精選詳解

When a rocket is traveling toward a mountain at 100 m/s, the sound waves from this rocket's engine approach the mountain at speed of V. If the rocket doubles its speed to 200 m/s, the sound waves from the engine will now approach the mountain at speed of \_\_\_\_.