Question

Natural length of spring is 60 cm and its spring constant is 4000 N/m. A mass of 20 kg is hung from it. The extension produced in the spring (take g=9.8m/s^2) is?

(a) 4.9cm

(b) 0.49cm

(c) 9.4cm

(d) 0.94cm

I have been asked this question at a job interview.

My question is based upon Periodic Motion topic in portion Oscillations of Engineering Physics I

Answer 1

Correct choice is (a) 4.9cm

To elaborate: In equilibrium, kx=mg

x=mg/k=(20×9.8)/9000=0.049m=4.9cm.