Answer
Hi,
An increase in amplitude from 3m to 6 m increases the energy it transports. The frequency of the wave is not affected
Explanation
Amplitude is the height of a wave where as frequency is the number of waves that pass by each second. A wave with bigger amplitude has more energy than a wave with smaller amplitude. A point where more waves pass contains more energy that is transferred every second. The change in the amplitude of a wave does not change its frequency. However, frequency is inversely related to the wavelength of a wave.
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Answer:
Constructive interference
Explanation:
Here, the medium is same, same wavelength, same frequency, same amplitude and same direction of propagation.
Let the intensity of waves be I which is same for both
The formula for the net intensity is

where, Ф be the phase difference
So, 
Here, IR is maximum so the interference is constructive in nature.
Answer:
b is the answer tennis ball
Answer
D.Diffraction
Explanation
Diffraction is a property that is experienced by waves when they come across a barrier when they are in motion.
The ways tends to curve behind the barrier. This is called diffraction of waves.
Now, sound is a wave and it also experience diffraction. . So the brother will be able to hear the sound due to diffraction