The acceleration of the first block (4 kg) is -9.8 m/s².
The given parameters:
- <em>Mass of the first block, m₁ = 4.0 kg</em>
- <em>Mass of the second block, m₂ = 2.0 kg</em>
The net force on the system of the two blocks is calculated as follows;

where;
- <em>T </em><em>is the tension in the connecting string due weight of the first block</em>

Thus, the acceleration of the first block (4 kg) is -9.8 m/s².
Learn more about net force on two connected blocks here: brainly.com/question/13539944
Answer:
a

b

Explanation:
From the question we are told that
The wavelength of the light is 
The distance of the slit separation is 
Generally the condition for two slit interference is

Where m is the order which is given from the question as m = 2
=> ![\theta = sin ^{-1} [\frac{m \lambda}{d} ]](https://tex.z-dn.net/?f=%5Ctheta%20%20%3D%20%20sin%20%5E%7B-1%7D%20%5B%5Cfrac%7Bm%20%5Clambda%7D%7Bd%7D%20%5D)
substituting values

Now on the second question
The distance of separation of the slit is

The intensity at the the angular position in part "a" is mathematically evaluated as
![I = I_o [\frac{sin \beta}{\beta} ]^2](https://tex.z-dn.net/?f=I%20%20%3D%20%20I_o%20%20%5B%5Cfrac%7Bsin%20%5Cbeta%7D%7B%5Cbeta%7D%20%5D%5E2)
Where
is mathematically evaluated as

substituting values


So the intensity is
![I = I_o [\frac{sin (0.06581)}{0.06581} ]^2](https://tex.z-dn.net/?f=I%20%20%3D%20%20I_o%20%20%5B%5Cfrac%7Bsin%20%280.06581%29%7D%7B0.06581%7D%20%5D%5E2)

The movement of the tectonic plates is caused by convection currents in Earth´s mantle.
Answer: A) convection currents in Earth´s mantle.