Question

The diameter of brass rod is 4mm. Young’s modulus of brass is 9×10^9 N/m^2. The force required to stretch 0.1% of its length is ___________

(a) 360πN

(b) 36N

(c) 36π×10^5 N

(d) 144π×10^3N

I got this question during an online interview.

My doubt stems from Elastic Limit in chapter Thermal Properties of Matter of Engineering Physics I

Answer 1

The correct answer is (a) 360πN

The explanation: ∆l/l=0.1/100

F=YA∆l/l=(Y×πr^2×∆l)/l

F=(9×10^9×π×(2×10^(-3))^2×0.1)/100 N=360πN.