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

#1

Wavelength = 13 km

it vibrates 10 times each minute

so the frequency is defined by the number of vibrations per second

$f = 10 per\: min$

$f = \frac{10}{60}$

now the speed of wave is defined as

$v = \lambda* f$

$v = 13* \frac{1}{6} = 2.2 km/s$

so here velocity of wave is 2.2 km/s

#2

Intensity of wave is directly proportional to the square of its amplitude

so we can say

$Intensity = k*(amplitude)^2$

k = constant

so if amplitude is doubled then its intensity will be increased by its square

so intensity is 4 times