Oscillations Questions

Starting from the origin, a body oscillates simple harmonically with a period of $2\text{s}$. After what time will its kinetic energy be $75\%$ of the total energy?

The maximum velocity of a particle executing simple harmonic motion with an amplitude $7\text{mm}$ is $4.4\text{m/s}$. The period of oscillation is:

A coin is placed on a horizontal platform which undergoes vertical simple harmonic motion of angular frequency $\omega$. The amplitude of oscillation is gradually increased. The coin will leave contact with the platform for the first time: