A mass of $2.9 \mathrm{~kg}$ is suspended from a string of length $50 \mathrm{~cm}$ and is at rest. Another…

A mass of $2.9 \mathrm{~kg}$ is suspended from a string of length $50 \mathrm{~cm}$ and is at rest. Another body of mass $100 \mathrm{~g}$, which is moving horizontally with a velocity of $150 \mathrm{~m} / \mathrm{s}$ strikes and sticks to it. Subsequently when the string makes an angle of $60^{\circ}$ with the vertical, the tension in the string is $\left(g=10 \mathrm{~m} / \mathrm{s}^2\right)$
  1. 145 N
  2. 135 N
  3. 125 N
  4. 90 N

Solution

From law of conservation of momentum, we known,
$ \begin{array}{lc} & m_1 u_1+m_2 u_2=m_1 v_1+m_2 v_2 \\ u_1=0, u_2=150 \mathrm{~m} / \mathrm{s}, m_1=2.9 \mathrm{~kg} \text { and } m_2=0.1 \mathrm{~kg} \\ \text { So, } & 2.9 \times 150=(2.9+0.1) \mathrm{v} \\ \Rightarrow & \frac{2.9 \times 150}{3}=v \\ \Rightarrow & \\ \text { Also, } & T \sin \theta=\frac{m v^2}{r} \end{array} $ Putting the values and solving, we get $T=135 \mathrm{~N}$

Asked in: AP EAMCET 2013

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