Saved Bookmarks
| 1. |
Earthwuakes generate sound waves inside the earth. Unilke 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 `kms^(-1)`. A seismograph records P and S waved from an earthquake. The first P wave arrives 4 min before the first S wave. Assuming the waves travel in straight line, how far away does the earthquake occur? |
|
Answer» Let `upsilon_(1), upsilon_(2)` be the velolcities of S waves P waves, and `t_(1), t_(2) ` be the time taken by these waves to travel to the position of seismograph. If l is the distance of occurrence of earthquake from the seismograph, then `l=upsilon_(1)t_(1)=upsilon_(2)t_(2)` ...(i) Now, `upsilon_(1)=4kms^(-1) and upsilon_(2)=8kms^(-1)` `:. 4t_(1)=8t_(2) or t_(1)=2t_(2)` ...(ii) Also, `t_(1)-t_(2)=4min=240s`. Usint (ii), `2t_(2)-t_(2)=240s, t_(2)=240s` `t_(1)=2t_(2)=2xx240=480s.` Now, from (i) `l=upsilon_(1)t_(1)=4xx480=1920km` Hence earthquake occurs 1920km away from the seismograph. |
|