A slightly conical wire of length L and end radii r1 and r2 is stretched by two forces F and F applied parallel to the length in opposite directions and normal to the end faces. If Y denotes Young's modulus, then the extension produced is:
A
FLπr1r2Y
Right on! Give the BNAT exam to get a 100% scholarship for BYJUS courses
B
FLYπr1r2
No worries! We‘ve got your back. Try BYJU‘S free classes today!
C
FLπr1Y
No worries! We‘ve got your back. Try BYJU‘S free classes today!
D
FLπr21Y
No worries! We‘ve got your back. Try BYJU‘S free classes today!
Open in App
Solution
The correct option is CFLπr1r2Y If R be the rate of increase of radius per length, R=r2−r1L Consider a element of thickness dx at a distance x from narrow end of the wire. The radius of the element is y=r1+Rx. The extension in the element is dl=Fdx(πy2)Y thus, l=FπY∫L0dxr1+Rx let r1+Rx=p,Rdx=dp or l=FπY∫r1+RL0dpRp2=FπYR[1r1−1r1+RL]=FπYR[r1+RL−r1r1(r1+RL)] or l=FLπY(r2−r1).r2−r1r1(r1+r2−r1)=FLπr1r2Y