Mechanics inclined plane question

[themster]

Homework Statement

A small object of mass m is given an initial velocity u at point A. Just after it passes B the reaction force between the object and the surface drops at half the previous value. If the coefficient of friction between the object and the surface is μ=0.3, find the initial velocity u.
ω0 =10rad/s
Ans: 2.46 m/s

Homework Equations

F = μR
Possibly SUVAT equations?

The Attempt at a Solution

 

[CWatters]

It's traditional for you to show you have made some attempt at the question.

Hints:
Why does the normal force after point B drop?
What's the definition of μ?