*! how does increasing the mass of a moving object would increase its velocity down the incline?

The mass of an object does not affect its speed along an inclined plane, presuming that the object's mass does not prevent it from moving altogether. Only the force of gravity, the angle of the incline and the coefficient of friction influence the object's speed.

a longitudinal wave moves energy that is to the direction of the wave’s movement. - true

0.11 m/s and 0.28 m/s should be correct