When the speed of the particle is close to that of light, it's observed mass would be infinitely large.
To answer the question, we need to know what observed mass is.
This is the mass the body of an object in relativistic motion appears to have.
So, observed mass, m' = m/√(1 - β²) where
Now, since the speed of the particle is close to that of light, β ≅ 1.
So, m' = m/√(1 - β²)
m' = m/√(1 - 1²)
m' = m/√(1 - 1)
m' = m/√0
m' = m/0
m' = ∞
So, when the speed of the particle is close to that of light, it's observed mass would be infinitely large.
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