I'm sure I'm being stupid, but I don't know where I'm going wrong on this question, could somebody help?
A suitcase of mass 10kg slides down a ramp which is inclined at an angle of 20 degrees to the horizontal. The suitcase is modelled as a particle and the ramp is a rough plane. The top of the plane is A. The bottom of the plane is C and AC is a line of greatest slope. The point B is on AC with AB=5m. The suitcase leaves A with a speed of 10 ms-1 and passes B with a speed 8 ms-1.
Find b) the coefficient of friction
So this is what I did:
to find deceleration of suitcase,
u=10 ms-1
a=8ms-1
s=5m
a=?
v^2=u^2 + 2as
64=100 + 10a
a= - 3.6 ms-2
Resolving perpendicular to plane,
R-10gsin20 = 0
R=10g sin20
Resolving parallel to plane,
-3.6 x 10 = 10gcos20 - F
F = 10 g cos 20 + 36
Plugging this into the formula Fmax = coefficient of friction x R
gives 3.82.
This answer, according to the mark scheme is 0.755. Please help!