A block, whose mass is $0\mathrm{.}680$ kg$,$ is attached to a spring with a force constant of $156$ N$/$m$.$ The block rests upon a frictionless, horizontal surface$.$

A block labeled m is attached to the right end of a horizontal spring, and the left end of the spring is attached to a wall. The spring is stretched horizontally such that the block is displaced by a distance A to the right of its equilibrium position.

The block is pulled to the right a distance A $=0\mathrm{.}140$ m from its equilibrium position $($the vertical dashed line$)$ and held motionless. The block is then released from rest.

$($a$\mathrm{) }$

At the instant of release, what is the magnitude of the spring force $($in N$)$ acting upon the block? 

 

$($b$\mathrm{) }$

At that very instant, what is the magnitude of the block's acceleration $($in m$/$s$2)?$

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