A steel rod of circular section tapers from $2 cm$ diameter to $1 cm$ diameter over a length of $50 cm.$ If the modulus of

elasticity of the material is $2 x {10}^6 kg/c{m}^2$, then the increase in length under a pull of 

• • 1

    $\frac{0.3}{2\pi }cm$

  • 2

    $\frac{30}{\pi }cm$

  • 3

    $\frac{300}{\pi }cm$

  • 4

    $750 cm$