Given an inclined angle of θ = 30° and 10m long. The coefficient of friction is 0,1 and the mas of the block is 1kg.
a) Find the velocity needed for the block to climb the plane and its velocity be 0 in the top.
b) Find the time it took to reach the top.
c) Find the speed of the block when it reaches the bottom after its descent.
I solved a) and c) already (10,7 m/s and 9m/s)
For a) and c) : Wr + Ec1 + Ep1 = Ec2 + Ep2 ===> u.m.g.cos θ.x + 1/2 m v1^2 + mgh1 = 1/2 m v2^2 + mgh2
For b) : Fr = uN ; Fr = ma ; fv = iv + a.t
The Attempt at a Solution
I think i've got to find the acceleration first. But i'm probably messing the equation. Supposedly the friction force (u.N) is equal to mass + acceleration, but im having second thoughts about if i have to add the weight projected on the x plane (m.g.cos ) ?
∑F = m.a
Fr = m.a
u.m.g.cos210 = m.a
u.g.cos210 = a
-0.84m/s^2 = a <===== Thats wrong i guess.
What am i missing?
Then i should use :
fv = iv + a.t
0 = 10.7m/s + a.t
(-10.7m/s)/a = t