A spring is hung vertically from a fixed point. A mass M is hung from the other end of the spring, as illustrated in the figure below.
The mass is displaced downwards and then released. The subsequent motion of the mass is simple harmonic.
The variation with time 
of the length 
of the spring is shown in the graph below.
State
one time at which the mass is moving with maximum speed
one time at which the spring has maximum elastic potential energy.
or 
or 
or 
or 
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or 
or 
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