Final answer:
The earliest time after the block is released that its kinetic energy is exactly one-half of its potential energy is determined by the characteristics of the oscillating system.
Step-by-step explanation:
In this scenario, we have a block attached to a horizontal spring that is pulled back and then released. We are asked to find the earliest time after the block is released that its kinetic energy is exactly one-half of its potential energy.
Based on the given information, the frequency of the block is 0.72 Hz. When the block is at its earliest time, the velocity and kinetic energy are equal to zero. At this point, the force on the block is equal to the positive value of the spring constant multiplied by the amplitude, and the potential energy stored in the spring is equal to the spring constant multiplied by the square of the amplitude.
The total energy of the system, which is the sum of the potential energy and the kinetic energy, remains constant throughout the oscillations. Therefore, at the point where the kinetic energy is one-half of the potential energy, the total energy is also unchanged.