NCERT/CBSE PHYSICS CLASS 11 textbook http://www.TutorBreeze.com Answers to NCERT/CBSE PHYSICS Class 11(Class XI)textbook
CHAPTER Fifteen
WAVES
EXERCISES
15.26 Earthquakes generate sound waves inside the earth. Unlike a gas, the earth can experience
both transverse (S) and longitudinal (P) sound waves. Typically the speed of S wave is about
4.0 km s–1, and that of P wave is 8.0 km s–1. A seismograph records P and S waves from an
earthquake. The first P wave arrives 4 min before the first S wave. Assuming the waves travel
in straight line, at what distance does the earthquake occur ?
Q.15.26 Speed of p‐wave = 8 km/s Speed of S‐=wave = 4 km/s Let total time taken by p wave to travel from the point where earthquake took place = t sec Now distance of the earthquake centre x = Vpt = Vs ( t + 4 ) ⇒ 8t = 4 ( t + 4 ) 8t − 4t = 16 4t = 16 t = 4 min So time taken by p wave to travel = 4 × 8 × 60 = 1920 km Please do not copy the answer given here Write to us for help