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5.Work, Energy, Power and Collision
normal
$A$ particle of mass $m$ is released from $a$ height $H$ on $a$ smooth curved surface which ends into a vertical loop of radius $R$, as shown The minimum value of $H$ required so that the particle makes a complete vertical circle is given by

A
$5 \,R$
B
$4\, R$
C
$2.5\, R$
D
$2\, R$
Solution
$N=\frac{m v’^{2}}{r}-m g$
$\frac{m v’^{2}}{r}=m g$
$v^{\prime}=\sqrt{g r}$
$0+0=-m g(h-2 R)+\frac{1}{2} m g r$
$=-m g h+2 m g R+\frac{1}{2} m g R$
$h-2 R+\frac{R}{2}=\frac{5 R}{2}$
$=2.5 R$
Standard 11
Physics