A student says that he had applied a force F = - k√x on a particle and the particle moved in simple harmonic motion. He refuses to tell whether k is a constant or not. Assume that he has worked only with positive x and no other force acted on the particle.

The student is applying force on the particle in positive x direction only. So the particle will move in x direction and it will increase the value of k also according to F = - k√x