Answer:11686.5 joules
Explanation:
elastic constant(k)=53N/m
extension(e)=21m
Elastic potential energy=(k x e^2)/2
Elastic potential energy=(53 x (21)^2)/2
Elastic potential energy=(53x21x21)/2
Elastic potential energy=23373/2
Elastic potential energy=11686.5
Elastic potential energy is 11686.5 joules
