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Q14.2: NCERT Physics - Part 2 WAVES 14.2 Solution: A stone dropped from the top of a tower of height 300 m…

⚠️ Common Exam Traps & Conceptual Pitfalls

Students often mistakenly treat the total time as a single variable in the kinematic equation or forget to add the separate time interval for sound propagation. Always calculate the free-fall time and the sound travel time independently, then sum them to find the total delay.

A stone dropped from the top of a tower of height 300 m splashes into the water of a pond near the base of the tower. When is the splash heard at the top given that the speed of sound in air is 340 m s__? (g = 9.8 m s__)

Step-by-Step Verified Solution

**Answer:** t=8.7 st = 8.7 \text{ s} **Step-by-Step Explanation:** For the stone's fall:
s=ut+12gt2  ⟹  300=0+12(9.8)t2s = ut + \frac{1}{2}gt^2 \implies 300 = 0 + \frac{1}{2}(9.8)t^2
t2=6009.8=61.22  ⟹  t=7.82 st^2 = \frac{600}{9.8} = 61.22 \implies t = 7.82 \text{ s}
Time for sound to travel up:
t′=300340=0.88 st' = \frac{300}{340} = 0.88 \text{ s}
Total time:
T=t+t′=7.82+0.88=8.70 sT = t + t' = 7.82 + 0.88 = 8.70 \text{ s}
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All Questions in this Chapter

Q14.1 Q14.2 Q14.3 Q14.4 Q14.5 Q14.6 Q14.7 Q14.8 Q14.9 Q14.10 Q14.11 Q14.12 Q14.13 Q14.14 Q14.15 Q14.16 Q14.17 Q14.18 Q14.19

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