At highest point A, vA=√7gr TA and TB are tensions in the string when particle is at highest position (A) and lowest position (B). ∴ At point A,At highest point A, ‌‌
mvA2
r
‌=TA+mg ⇒‌‌
m(√7gr)2
r
‌=TA+mg ⇒‌7mg‌=TA+mg ⇒TA‌=6mg At point B by the law of conservation of energy, change in potential energy = Change in kinetic energy ‌mg(2r)=‌
1
2
mvB2−‌
1
2
mvA2 ⇒‌‌2mgr=‌
1
2
mvB2−‌
1
2
m(7gr) ⇒‌‌4gr=vB2−7gr ⇒‌‌vB=√11gr At lowest point B,TB−‌