A flatcar of mass \(m_{0}\) starts moving to the right due to a constant horizontal force F (Fig. 1.46). Sand spills on the flatcar from a stationary hopper. The velocity of loading is constant and equal to \(\mu \) \(\mathrm{kg} / \mathrm{s}\). Find the time dependence of the velocity and the acceleration of the flatcar in the process of loading. The friction is negligibly small.