A bob hangs from a rigid support by an inextensible string of length l . It is released from rest when string makes an angle 60o with vertical. The speed of the bob at the lowest position is

Question

A bob hangs from a rigid support by an inextensible string of length l . It is released from rest when string makes an angle 60o with vertical. The speed of the bob at the lowest position is (A) √g l (B) √3 g l (C) √2 g l (D) √5 g l

Tardigrade Admin · Accepted Answer

<img class="img-fluid question-image" alt="Solution" src="https://cdn.tardigrade.in/q/nta/p-ycniaagmobn1.png" /> This mean h=l(1 - cos (60)o) ⇒ h=l× (1/2) Velocity of bob v=√2 g h ⇒ v text = √2 g (l/2) ⇒ v = √g l

Q. A bob hangs from a rigid support by an inextensible string of length $l$ . It is released from rest when string makes an angle $6 0^{o}$ with vertical. The speed of the bob at the lowest position is

$g l$

$3 g l$

$2 g l$

$5 g l$

This mean $h = l (1 - cos (60)^{o})$
$\Rightarrow h = l \times \frac{1}{2}$
Velocity of bob $v = 2 g h$
$\Rightarrow v = 2 g \frac{l}{2}$
$\Rightarrow v = g l$

Q. A bob hangs from a rigid support by an inextensible string of length l . It is released from rest when string makes an angle 60o with vertical. The speed of the bob at the lowest position is

gl​

3gl​

2gl​

5gl​