Two beams of coherent light travel different paths, arriving at point P. If the destructive interference is to occur at point P, what should be the path difference between the two waves

Explanation:

When two coherent light beams travel different paths and arrive at a point , there will be difference in the length of path travelled by them . If this difference is zero then both will reinforce each other and their brightness will add up . Hence there will be constructive interference .

If their path difference is not zero but it is equal to odd multiple of their half wavelength like λ / 2 , 3 λ / 2 , 5 λ /2 , 7 λ /2 etc , then instead of reinforcing each other , they will destroy each other . This is called destructive interference . As a result of it , darkness will prevail at the point where they meet or interfere.

what is the speed of a softball that travels 20m in 2secs

speed = 20/2 = 10 m/s