A pendulum bob is hanging from the roof of an elevator with the help of a light string. When the elevator moves up with uniform acceleration ‘a’ the tension in the string is T₁ .When the elevator moves down with the same acceleration, the tension in the string is T₂ .If the elevator were stationary, the tension in the string would be

• A

  $\frac{{\mathrm{T}}_1+{\mathrm{T}}_2}{2}$

• B

  $\sqrt{{\mathrm{T}}_1+{\mathrm{T}}_2}$

• C

  $\frac{{\mathrm{T}}_1{\mathrm{T}}_2}{{\mathrm{T}}_1+{\mathrm{T}}_2}$

• D

  $\frac{2{\mathrm{T}}_1{\mathrm{T}}_2}{{\mathrm{T}}_1+{\mathrm{T}}_2}$