If a proton of mass m is moving with the velocity of light, its mass will be ______

  1. unchanged
  2. large but finite
  3. infinite
  4. zero

Answer (Detailed Solution Below)

Option 3 : infinite
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CONCEPT:

In the special theory of relativity, there are few unique ideas that completely change our understanding of physics. A few of the postulates or rules are as follows.

According to the Theory of Special Relativity:

1). The Laws of physics remain the same for all observers who are non-accelerating (i.e. not in motion).

2). The speed of light in the vacuum is completely independent of the observer's motion.

3). No particle which carries energy and has a mass can travel at the speed of light.

4). The most amazing idea is that the perception of time will change in every frame of reference.

5). According to Einstein's special theory of relativity, the mass of a particle increases with the increase in its velocity as

\(m = \frac{{{m_o}}}{{\sqrt {1 - \frac{{{v^2}}}{{{c^2}}}} }}\)
Where mo = rest mass of the particle, v = velocity of charged particle and c = speed of light

EXPLANATION:

According to the special theory of relativity, if v(velocity of the proton) becomes c(speed of light) then:

\(\Rightarrow m = \frac{{{m_o}}}{{\sqrt {1 - \frac{{{v^2}}}{{{c^2}}}} }}=\frac{{{m_o}}}{{\sqrt {1 - \frac{{{c^2}}}{{{c^2}}}} }}=\infty\)

Mass of the proton (m) will become infinity.

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