Archerfish are tropical fish that hunt by shooting drops of water from their mouths at insects above the water's surface to knock them into the water, where the fish can eat them. A 65 gg fish at rest just at the surface of the water can expel a 0.30 gg drop of water in a short burst of 5.0 msms. High-speed measurements show that the water has a speed of 2.5 m/sm/s just after the archerfish expels it.
A) What is the speed of the archerfish immediately after it expels the drop of water?

Speed = 0.012 m/s

Explanation:

We are given;

Mass of fish = 65g = 65 x 10^(-3)kg

Mass of water it can expel = 0.3g = 0.3 x 10^(-3)kg

Speed of water = 2.5 m/s

Since there is no external force given in fish drop system, linear momentum is conserved. From conservation of linear momentum;

m1v1 = m2v2

So,

65 x 10^(-3) x V1 = 0.3 x 10^(-3) x 2.5

V1 = 0.3 x 2.5/65 = 0.012 m/s

less than one you can't create energy

electromagnetic shielding is the practice of reducing the electromagnetic field in a space by blocking the field with barriers made of conductive or magnetic materials. shielding is typically applied to enclosures to isolate electrical devices from their surroundings, and to cables to isolate wires from the environment through which the cable runs. electromagnetic shielding that blocks radio frequency electromagnetic radiation is also known as rf shielding.

the shielding can reduce the coupling of radio waves, electromagnetic fields and electrostatic fields. a conductive enclosure used to block electrostatic fields is also known as a faraday cage. the amount of reduction depends very much upon the material used, its thickness, the size of the shielded volume and the frequency of the fields of interest and the size, shape and orientation of apertures in a shield to an incident electromagnetic

from wikipedia