(a)[2]
Because the plane is smooth, apply an energy method to determine the particle’s speed at $B$.
(b)[3]
Instead, suppose the plane is rough and the particle arrives at $B$ with speed $8\,\text{m s}^{-1}$. The plane has length $25\,\text{m}$, and the constant frictional force has magnitude $F\,\text{N}$. Determine the value of $F$.