Question

A load W produces an extension of 1mm in a thread of radius r. Now if the load is made 4W and radius is made 2r all other things remaining same, the extension will become

• A. 4 mm
• B. 16 mm
• C. 1 mm
• D. 0.25 mm

Answer 1

Answer: (C)

1 mm

Answer 2

$l = \frac { F L } { A Y } \therefore l \propto \frac { F } { r ^ { 2 } }$

$\frac { l _ { 1 } } { l _ { 2 } } = \frac { F _ { 2 } } { F _ { 1 } } \left( \frac { r _ { 1 } } { r _ { 2 } } \right) ^ { 2 } = ( 4 ) \times \left( \frac { 1 } { 2 } \right) ^ { 2 } = 1$∴$l _ { 2 } = l _ { 1 } = 1 \mathrm {~mm}$