SAVE MY LIFE - PHYSICS HELP NEEDED - Wooden Block?

Question

A wooden block of mass m = 9 kg starts from rest on an inclined plane sloped at an angle q from the horizontal. The block is originally located 5m from the bottom of the plane.

If the block, undergoing constant acceleration down the ramp, slides to the bottom in t = 2 s, and q = 30°, what is the magnitude of the kinetic frictional force on the block?

Answer 1

net Force = (mg sin 30º-friction force) so

if acceleration is a
e= 1/2a*t^2 so a= 2*5/4 =5/2 m/s^2
9*5/2 =(9*9.8*1/2-f)
so f=1/2I9*5-9*9.8I= 21.6 N directed against movement

Answer 2

42