Acceleration Questions

A particle of mass $0.3\text{ kg}$ is subjected to a force $F=-kx$ with $k=15\text{ N/m}$. What will be its initial acceleration if it is released from a point $20\text{ cm}$ away from the origin?

If $x$, $v$ and $a$ denote the displacement, the velocity and the acceleration of a particle executing simple harmonic motion of time period $T$, then, which of the following does not change with time?

A particle has an initial velocity $3\hat{i}+4\hat{j}$ and an acceleration of $0.4\hat{i}+0.3\hat{j}$. Its speed after $10\text{s}$ is: