about physics..?

Question

a brick slides down an inclined plank at a constant speed when the plank is inclined at an angle theta_0. if the angle is increased to theta_1, the block accelerates down the plank with acceleration a. the coefficient of the kinetic friction is the same in both cases.
given the two theta, calculate a.

Answer 1

gsinθ0 - μgcosθ0 = 0
gsinθ1 - μgcosθ1 = a
tanθ1 = μ
a = g(sinθ1 - tanθ0cosθ1)
or
a = gcosθ1(tanθ1 - tanθ0)