Once the box begins to slide and accelerate, kinetic friction acts to slow the box with a coefficient of kinetic friction μ_k = 0.1. The raised end of the surface can be lowered to a point where the box continues sliding but does not accelerate. The critical angle at which this happens,θ_c', can be found from the equation tan θ_c' = μ_k.

(a) What is this critical angle for the box?

(b) If the box is 5 ft from the pivot point, at what height will the box stop accelerating?