Alens focuses light at a single point called the focal point. what is responsible for the light rays coming together at the focal point?

The answer is; refraction.

When waves, including light, pass through two media with different densities, the waves bend at the transition between the two media due to differences in speed and wavelength. Convex lenses bend (refract) light and  concentrate it at one point called the focal point.

Force = mass × acceleration

9 = 65 x acceleration

acceleration= 9/65 = 0.318 m/s2