Q$3$: $[$Last one$]$ This question is better solved by applying Energy method.

The $250-$g pellet is pushed against the spring at A and released from rest. It moves along a $1\mathrm{.}2$ m rough horizontal section, then into a smooth $600$ mm radius vertical loop. On the rough surface, $\backslash (\backslash$mu$\_\{$k$\}=0\mathrm{.}3\backslash )$ and the distance travelled is $1\mathrm{.}2$ m $.$ The spring is initially compressed $75$ mm $.($a$)$ What is the minimum speed of the pellet at D and $($b$)$ What is the minimum spring constant $\backslash ($ k $\backslash )$ for which the pellet remains in contact with the loop?