As the block is sliding down with constant velocity. Therefore friction force along the slope must be equal to the component of gravity along the slope.
μN = mgsin0
umgcose mgsine
=
μ = tane
When thrown up: Initial Velocity is Vo
Acceleration (both friction and
component of gravity acting downwards the slope as relative motion
is upwards) is µN + mgsin0 = tanmgcose +
mgsin0 = 2mgsin
Final Velocity is zero.
Therefore distance traveled up the incline is:
v² - u² = 2as
⇒ 0-V₂² =2(-2mgsin0)s
S = 4mgsin