Doubt from AskPhysics.com
I have heard the following statements->
1. Quarks always exist in a group of 2 or 3, and can not stand alone.

2. Protons are made up of 2 up quarks, and 1 down quark.

3. Quantum mechanics allows us to entangle a particle by somehow dividing it into 2(For example, if a proton’s energy is 5 joules, if we split into 2 then sum of both splitted particles will have energy sum of 5 joules.)

Aren’t the statements contradicting each other? Please tell me correct if anyone of my statement is incorrect. Thank You!

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The basic concepts of relativity are explained in a very simplified way that are easy to understood by Mr. Vivek Sawhney in this YouTube Video… The video focuses upon the general discussion on Theory of Relativity….What is the theory of Relativity? What is time dilation and length contraction?

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A boy plays with a ball on a field surrounded by a fence which has a height of 2.5m . He kicks the ball vertically up from a height of 0.4m with a speed of 14 ms−1. (a) What is the maximum height of the ball above the fence? (b) What is the time taken to reach the maximum height? (c) How long is the ball above the height of the fence? (d) What is the velocity of the falling ball at the height of the fence? (e) What the acceleration of the ball after 1s ?

Asked John

Answer:

(a)

u=14 m/s

v=0 m/s at max height

Combination of Errors in a series of Measurements

Suppose the values obtained in several measurement are a1, a2, a3, …, an.

Arithmetic mean, amean = (a1+ a2 + a3+ … + an)/n

o Absolute Error: The magnitude of the difference between the true value of the quantity and the individual measurement value is called absolute error of the measurement. It is denoted by |Δa| (or Mod of Delta a). The mod value is always positive even if Δa is negative. The individual errors are:

Δa1 = amean – a1, Δa2 = amean – a2, ……. ,Δan = amean – an

o Mean absolute error is the arithmetic mean of all absolute errors. It is represented by Δamean.

Δamean = (|Δa1| + |Δa2| +|Δa3| + …. +|Δan|) / n

For single measurement, the value of ‘a’ is always in the range amean± Δamean

So, a = amean ± Δamean Or amean – Δamean< a <amean + Δamean

o Relative Error: It is the ratio of mean absolute error to the mean value of the quantity measured.

Relative Error = Δamean / amean

o Percentage Error: It is the relative error expressed in percentage. It is denoted by δa.

δa = (Δamean / amean) x 100%

Combination of Errors

If a quantity depends on two or more other quantities, the combination of errors in the two quantities helps to determine and predict the errors in the resultant quantity. There are several procedures for this.

Suppose two quantities A and B have values as A ± ΔA and B ± ΔB. Z is the result and ΔZ is the error due to combination of A and B.

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