A block of mass $1.4$ $kg$ is on an incline with angle $\theta = 18^o$ (Fig. 1). The block is pushed against a spring so that the spring is compressed by $0.21$ $m$. The spring constant is $96$ $N/m$ and the block is not attached to the spring.
The spring is suddenly released and it pushes the block up the incline. The block stops after traveling $0.32$ $m$ along the incline (Fig. 2).
How much is the coefficient of kinetic friction between the block and the incline?