At a definite point, the bridge would begin oscillating to the matching rhythm as that
of the marching footsteps.
This oscillation would touch a determined peak when the bridge can
no longer tolerate its own
power and later collapses. So, soldiers are
systematic to break their steps
while passing a bridge.
When two bodies collide with each other in the absence of an external force, then the total final momentum of the bodies is equal to their total initial momentum.
Answer:
iv) It is 9x bigger than before
Explanation:
As the amplitudes of the new speakers add directly with the original one, taking into account the phase that they have, the composed amplitude of the sound wave is as follows:
At = A + 4A -2A = 3 A
The intensity of the wave, assuming it propagates evenly in all directions, is constant at a given distance from the source, and can be expressed as follows:
I = P/A
where P= Power of the wave source, A= Area (for a point source, is equal to the surface area of a sphere of radius r, where is r is the distance to the source along a straight line)
For a sinusoidal wave, the power is proportional to the square of the amplitude, so the intensity is proportional to the square of the amplitude also.
If the amplitude changes increasing three times, the change in intensity will be proportional to the square of the change in amplitude, i.e., it will be 9 times bigger.
So, the statement iv) is the right one.
The Electromagnetic ave that is about the size of humans is : A typical micro waves have around 14 inches ( 1.1 meter) in height.
This is very similar to the height of human right before we hit puberty (around 9 - 10 years old)
