Question

If an earthquake wave having a wavelength of 13 km caused the ground to vibrate 10 times each minute, what is the speed of the wave?
1.2 km/s
2.2 km/s
220 m/s
22 m/s

If the amplitude in a sound wave is doubled, by what factor does the intensity of the wave increase?
2
1
8
4(my choice)

Answer 1

period = 60/10 = 6 seconds
goes 13 km in 6 seconds
13/6 = 2.2 km/s

yes, 2^2 = 4

Answer 2

F = 10vib/min = 10vib/60s = 1/6 vib/s = Freq.
T = 1/F = 1/(1/6) = 6 s. = Period.
Wavelength = V*T= 13.
V * 6 = 13,
V = 2.2 km/s.