A large goose lands in a lake and bobs up and down for a short time. A fisherman notices that the first wave crest created by the goose reaches the shore 7.3 s after the goose first contacts the water. The distance between two wave crests is 65 cm, and in 1.9 s he sees four wave crests hit the shore. How can the fisherman use these observations to determine how far from the shore the goose landed?

0.55x745.7j and a calculator

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

3. dark matter

empty space could also be a simple vacuum