RAJASTHAN PMT Rajasthan - PMT Solved Paper-2004

  • question_answer
    A spring executes SHM with mass of 10 kg attached to it. The force constant of spring is 10Nm. If at any instant its velocity is 40 cm/sec, the displacement will be (where amplitude is 0.5m):

    A)  0.09 m                                 

    B)  0.3 m

    C)  0.03 m                 

    D)         0.9 m

    Correct Answer: B

    Solution :

    Time period of spring is given by \[T=2\pi \sqrt{\left( \frac{m}{k} \right)}\] \[\Rightarrow \]               \[\omega =\frac{2\pi }{T}=\sqrt{\left( \frac{k}{m} \right)}\] \[\therefore \]  \[\omega =\sqrt{\left( \frac{10}{10} \right)}=1\] Velocity of mass at displacement\[x\]                                 \[u=\omega \sqrt{{{a}^{2}}-{{y}^{2}}}\] \[\Rightarrow \]               \[{{y}^{2}}={{a}^{2}}=\frac{{{u}^{2}}}{{{\omega }^{2}}}\]                                    \[={{(50)}^{2}}-\frac{{{(40)}^{2}}}{{{1}^{2}}}\]                                       \[={{(50)}^{2}}-{{(40)}^{2}}\]                                       \[=(50+40)(50-40)=900\] \[\therefore \]     \[y=30\,cm=0.3\,m\]


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