When light travels from a medium with higher refractive index to a medium with lower refractive index, there is a critical angle after which all the light is reflected (so, there is no refraction).
The value of this critical angle can be derived by Snell's law, and it is equal to

where n2 is the refractive index of the second medium and n1 is the refractive index of the first medium.
In our problem, n1=1.47 and n2=1.33, so the critical angle is
Answer:
The change in the mass of box = 0.01 kg
Volume of air in the polythene bag = Volume of air in the rigid box
Therefore, Volume of air in the box = 0.008 m^3
Now, Density = Mass/ Volume
=> Density = 0.01 / 0.008 = 1.25 Kg / m^3
Explanation:
I looked it up
It's very hard to see the self-portrait, so I can't identify him.
We know that the change in momentum is equals to the product of force and time that is impulse (
). Therefore, we need to determine the value of that the water is in air by using the second equation of motion,

Here, u is initial velocity which is zero.
.
Thus, impulse

From Newton`s second law,

Therefore, impulse

Given,
and 
Substituting these values, we get
Change in momentum = impulse
.