When light travels from a medium with higher refractive index into a medium with lower refractive index, there is a maximum angle (called critical angle) for which all the light is reflected, so there is no refraction.
The value of the critical angle is given by:
when n1 is the refractive index of the first medium, while n2 is the refractive index of the second medium. In our case, n1=1.33 (the water) and n1=1.00 (the air). Putting numbers in, we get
Answer
given,
mass of the shell = 87 g = 0.087 Kg
speed of the muzzle = 853 m/s
mass of the helicopter = 4410 kg
A burst of 176 shell fired in 2.93 s
resulting average force = ?
momentum of the shell = m v
= 0.087 x 853
= 74.21 kgm/s
momentum of 176 shell is = 176 p
= 176 x 74.21
= 13060.96
momentum of helicopter = - 13060.96 kgm/s
amount of speed reduce a = 
a= 
a = 2.96 m/s²
velocity = \dfrac{2.96}{2.93}
v = 1.01 m/s
A. 9 J
In a force-distance graph, the work done is equal to the area under the curve in the graph.
In this case, we need to extrapolate the value of the force when the distance is x=30 cm. We can easily do that by noticing that there is a direct proportionality between the force and the distance:
where k is the slope of the line. We can find k, for instance chosing the point at x=5 cm and F=10 N:
And now we can calculate the work by calculating the area under the curve until x=30 cm, F=60 N:
B. 24.5 m/s
The mass of the arrow is m=30 g=0.03 kg. The kinetic energy of the arrow when it is released is equal to the work done by pulling back the bow for 30 cm:
where m is the mass of the arrow and v is its speed. By re-arranging the formula and using W=9 J, we find the speed:
