What will occur when the trough of wave a overlaps the trough of wave b?

Constructive interference                  

Explanation:

The superposition of two wave is called interference phenomenon. After interference of wave, the amplitude of resultant wave can be more, less or remains the same.

The two conditions of interference are :

1. Constructive interference      2. Destructive interference  

According to given question, when the trough of wave A overlaps the trough of wave B constructive interference occurs. The amplitude of resultant wave is greater than the individual waves. Also, the energy of the resultant wave is more than the energies of wave A and wave B.

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explanation:

the minimum constant speed at which she can catch the train is 2.7 m/s

given:

acceleration = 0.6

time = 4.5 s

to find:

velocity = ?

formula used:

from 1st kinematic equation we get,

v = u + at

u = initial speed of train = 0 m/s

v = final speed of the train

a = acceleration of the train

t = time

solution:

from 1st kinematic equation we get,

v = u + at

u = initial speed of train = 0 m/s

v = final speed of the train

a = acceleration of the train

t = time

v = 0 + (0.6 × 4.5)

v = 2.7 m/s

the minimum constant speed at which she can catch the train is 2.7 m/s