At what speed will a 2.0 kg object have a mass of 6.0 kg?

Answer 1

As we know the mass-energy equivalence relation,

m=m_o/√(1-v²/c²) (1)

here, m = 6 kg and m_o=2 kg

Put these values in equation 1

we get 6=2/√(1-v²/c²) ⇒ 3=1/√(1-v²/c²)

1-v²/c²=1/9 ⇒ v=2√2/3