B) moves with a constant speed until hitting the other end.
Answer:
649.8420 nm
Explanation:
We have given 
we have to find unknown wavelength that is 
The condition for constructive interference is 
Where d is distance between slits
is angle of emergence and n is order of maxima
Using constructive interference equation
---------eqn 1
---------eqn 2
On dividing eqn 1 by eqn 2


Yes i think since action force means moving in one direction