An Earthquake Generates Three Kinds of Waves: Surface Waves (L-Waves),which

Multiple Choice

An earthquake generates three kinds of waves: surface waves (L-waves) ,which are the slowest and weakest,shear (S) waves,which are transverse waves and carry most of the energy,and pressure (P) waves,which are longitudinal waves and are the fastest.The speed of P waves is approximately 7 km/s,and that of S waves is about 4 km/s.People do not generally feel the P waves,but animals seem to be sensitive to them.If a person reports that her dog started barking 20 seconds "before the earthquake," then approximately how far was the origin of the earthquake?

A) 100 km
B) 200 km
C) 300 km
D) 400 km
E) 500 km