21. When a 4 kg mass is hung vertically on a light spring that obeys Hooke’s law, the spring stretches by 2 cms. The work required to be done by an external agent in stretching this spring by 5 cms will be

21. When a 4 kg mass is hung vertically on a light spring that obeys Hooke’s law, the spring stretches by 2 cms. The work required to be done by an external agent in stretching this spring by 5 cms will be(g=9.8 m/sec²)

(a)   4.900 joule                                     (b)   2.450 joule

(c)   0.495 joule                                      (d)   0.245 joule

Answer-b

(5)