The block slides on the incline when mgsinθ ≥ μmgcosθ ⇒ tan θ ≥ μ ⇒ tanθ ≥ 3 =1.732
For the block to topple, we have f (
15
2
) ≥ N (5) (about centre of masss) ⇒ µN (
15
2
) ≥ N (5) ⇒ µ ≥
2
3
= 0.67 or tan θ ≥ 0.67 That is, the block neither slides nor topples till θ ≤ tan−1 (0.67) (i.e. it remains at rest) and on exceeding this, it topples first before sliding.