A round box of inner diameter D containing a washer of radius r lies on a table (Fig). The box is moved as a whole at a constant velocity v directed along the lines of centres of the box and the washer. At an instant `t_(0)`, the washer hits the box. Determine the time dependeces of the displacement `x_("wash")` of the waher and of its velocity `v_("wash")` relative to the table, starting from the instant `t_(0)` and assuming that all the impacts of the washer against the box are perfectly elastic. Plot the graphs `x_("wash")(t)` and `v_("wash")(t)`. The friction between the box and the washer should be neglected.