Question

in a cross hole test, the trigger and geophones are 5m apart. after impact, the arrival time of sv wave at geophone is 20 msec. the velocity of sv wave is (a) 200 m/sec (b) 300m/sec (c) 250m/sec (d) 350 m/sec

Answer 1

t = arrival time for sv wave = 20 m sec = 20 x 10⁻³ sec

( 1 milli = 10⁻³ )

d = distance between trigger and geophones = 5 m

v = speed of sv wave

Formula for speed  

v = d/t

v = 5 m/(20 x 10⁻³ sec)

v = 250 m/s

option c is correct.

Answer 2

distance between trigger and geophone, d = 5m
the time taken to arrive so wave at geophone , t = 20msec = 20 × 10^-3 sec
[as we know, 1mili sec = 10^-3 sec]

now, speed of sv wave = distance between trigger and geophone/time taken to arrive sv wave at geophone
= 5/{20 × 10^-3}
= 5000/20 = 250 m/s

hence, option (c) is correct choice