You stand on a pier watching water waves and see 10.9 waves pass by in a time of 28 seconds. What is the frequency of the water waves?

0.4Hz

Explanation:

Given parameters:

   Number of waves  = 10.9waves

   Time taken  = 28s

Unknown:

Frequency of water waves = ?

Solution:

The frequency of a wave is the number of waves that passes through a point per unit of time.

  Frequency  =

  Insert parameters and solve;

         Frequency  =   = 0.4Hz

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

answer: 2×10^-2kg

explanation: density= mass per volume

vol=mass/density

converting to s.i units we have;

3÷1000kg = 0.003

1.5÷100m = 0.15

0.003/0.15 = 0.02kg