What type of energy is stored by a spring when it is stretched?
Internal mechanical energy
Gravitational potential energy 
Excitation energy
Elastic potential energy
Elastic potential energy is energy stored as a result of applying a force to deform an elastic object. The energy is stored until the force is removed and the object springs back to its original shape, doing work in the process. Many objects are designed specifically to store elastic potential energy, for example: The coil spring of a wind-up clock.  An archer's stretched bow. 
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Internal mechanical energy
Gravitational potential energy 
Excitation energy
Elastic potential energy
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