Question

One end of the string is pulled with constant velocity $v$ as shown in figure, then velocity of block will be :

• A. $v\sin \theta$
• B. $v\sec \theta$
• C. $v\tan \theta$
• D. $\frac{v}{\sin \theta }$

Answer 1

The correct option is B $v\sec \theta$

The length of string between pulley and mass ${}^{\prime }{m}^{\prime }$ must remain constant, and it is only possible when component of velocity of the block along the length of string is equal to velocity at which string is pulled i.e $v$.
$\Rightarrow v^{\prime }\cos \theta =v$
$\therefore v^{\prime }=\frac{v}{\cos \theta }=v\sec \theta$