The spring potential energy is 1.6 J
Explanation:
The elastic potential energy of a spring is given by the equation:

where
U is the potential energy
k is the spring constant
x is the compression/stretching of the spring
For the spring in this problem, we have:
x = 40 cm = 0.40 m is the stretching
k = 20 N/m is the spring constant
Substituting into the equation, we can find the spring potential energy:

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Answer:
The focal length is 
The radius of curvature is 
Explanation:
From the question we are told that
The magnification of the mirror is 
The distance of the person from the mirror(the object distance ) is 
The negative sign shows that it is been placed in front of the mirror
Generally the magnification of the mirror is mathematically represented as

=> 
=> 
Generally from the lens equation we have that

=> 
=> 
Generally the radius of curvature is mathematically represented as

=> 
=> 