Question

6. A small bob of mass 2 kg is suspended from an
inextensible string as shown in figure. If length of
string is l = 5 m and bob is given an initial
horizontal velocity u = 10 m/s, then the speed of
bob when string is inclined at angle 90° with the
vertical will be
(1) 20 m/s
(3) 2 m/s
(2) 5 m/s
(4) Zero​

Answer 1

$\huge{\underline{\underline{.........Answer.........}}}$

$\huge{\underline{ Given :-}}$

(This the case of vertical circle motion)

m = 2 kg.

l = 5 m.

u = 10m/s.

${\theta = 90 degrees}$

$\huge{\underline{ Explanation:- }}$

From the formula of velocity

$v = \sqrt{ {u}^{2} - 2gl(1 - cos \: \theta} )$

substituting the values in the above equation.

$v = \sqrt{100 - 2 \times 10 \times 5}$

as cos 90 is zero.

$v = \sqrt{100 - 100}$

$v = \sqrt{0}$

$v = 0$

$\boxed{\boxed{v = 0 m/s - option -- (4)}}$

So,the speed of the bob when it makes an angle 90° with the vertical is Zero.

#refer the attachment for figure.