Explanation:
It is given that,
Wavelength of monochromatic light, 
Slits separation, 
(a) We need to find the angle corresponding to the first bright fringe. For bright fringe the equation is given as :
, n = 1



(b) We need to find the angle corresponding to the second dark fringe, n = 1
So, 




Hence, this is the required solution.
This suggest the the atom has a very small positively charged nucleus in the mass of the atom is concentrated.
And the electrons revolves around the nucleus in their orbits.
Its about momentum. Momentum (p)=mass(m)xvelocity(v)
So for the first ball P=4x8=32kgm/s
For the second the momentum is zero as it is still.
So overall momentum its 32kgm/s
Momentum has to be conserved
After the collision the momentum of the 4kg ball is 4x4.8=19.2kgm/s
As momentum is conserved 32-19.2=12.8kgm/s remaining
So rearrange for velocity so v=p/m=12.8/1=12.8m/s for the 1kg ball
When the kinetic energy is transformed into another for of energy during the collision or impact