How fast would a 4.8 kg object slide down a frictionless incline of 10.3 degrees?

infinitely fast, constant acceleration forever

m a = m * 9.81 * sin 10.3
so
a = g sin 10.3 = 9.81 sin 10.3
so
v = (9.81 sin 10.3) t
v is proportional to time, forever