Electromagnets are used for various purposes but I fathom in this instance, the questioner is asking about how electromagnetics can be used to attraction or repulsion.
Example, electromagnets are used for attraction in cranes which attach them to containers in order to lift them.
Meanwhile, Maglev trains use electromagnets repulsive properties.
Another name for these two words is "constant" and you want to have a "constant", because you want something to compare your experimental group to, to see whether data had changed or not. So you have placebos or a double- blind to compare your experimental group to it and also so you know you don't have a bias or anything in the study.
Answer:
The time taken to stop the box equals 1.33 seconds.
Explanation:
Since frictional force always acts opposite to the motion of the box we can find the acceleration that the force produces using newton's second law of motion as shown below:

Given mass of box = 5.0 kg
Frictional force = 30 N
thus

Now to find the time that the box requires to stop can be calculated by first equation of kinematics
The box will stop when it's final velocity becomes zero

Here acceleration is taken as negative since it opposes the motion of the box since frictional force always opposes motion.
To solve this problem we will apply the concepts of linear mass density, and the expression of the wavelength with which we can find the frequency of the string. With these values it will be possible to find the voltage value. Later we will apply concepts related to harmonic waves in order to find the fundamental frequency.
The linear mass density is given as,



The expression for the wavelength of the standing wave for the second overtone is

Replacing we have


The frequency of the sound wave is



Now the velocity of the wave would be



The expression that relates the velocity of the wave, tension on the string and linear mass density is





The tension in the string is 547N
PART B) The relation between the fundamental frequency and the
harmonic frequency is

Overtone is the resonant frequency above the fundamental frequency. The second overtone is the second resonant frequency after the fundamental frequency. Therefore

Then,

Rearranging to find the fundamental frequency



Answer:
a) 4
b) 2
c) 8
Explanation:
In a cubic lattice, each atom of the vertex is shared among other 8 unit cells, so the atoms on the vertex contribute to 1/8 to a given unit cell.
a) Ina face-centered cubic we have 8 atoms on the vertex and one in each face, which is shared with another unit cell, so it contribute to 1/2
Therefore, the total atoms are:
8*(1/8) + 6*(1/2) = 4
b) In the body centered cubic structure, the centered atom is not shared with another cell, therefore it contribute to 1 to the given cell:
The number of atoms per unit cel is:
8*(1/8) + 1 = 2
c) The diamond lattice is similar to the face-centered cubic lattice but it contains two identical atoms per lattice point.
Therefore it must contain twice atoms than the face-centered cubic lattice:
that is, it has 8 atoms per unit cell