A light elastic string of natural length 2.0 m is stretched to a total length of 3.0 m, storing 18 J of elastic potential energy.
The string is then stretched further to a total length of 5.0 m. Assuming Hooke's law is obeyed, what is the elastic potential energy now stored in the string?
30 J30\text{ J}30 J
50 J50\text{ J}50 J
54 J54\text{ J}54 J
162 J162\text{ J}162 J