Question

In the figure the string has a mass $4.5\text{g}$. How much time will it take for a transverse disturbance produced at the floor to reach the pulley ?
(Take $g=10{\text{ms}}^{-2}$ and assume that tension in the string is constant throughout)

• A. $0.04\text{s}$
• B. $0.2\text{s}$
• C. $0.4\text{s}$
• D. $0.02\text{s}$

Answer 1

The correct option is D $0.02\text{s}$


For given string mass per unit length is $\mu =\frac{4.5\times {10}^{-3}}{2.25}=2\times {10}^{-3}$
Speed of wave in the string is
$v=\sqrt{\frac{T}{\mu }}=\sqrt{\frac{20}{2\times {10}^{-3}}}=100{\text{ms}}^{-1}$

Using Kinematics equation,
$s=ut$
$2=100t$
$t=0.02\text{s}$