JEE Main & Advanced Physics Work, Energy, Power & Collision / कार्य, ऊर्जा और शक्ति Question Bank Self Evaluation Test - Work, Energy and Power

  • question_answer
    A block of mass \[m=0.1\] kg is connected to a spring of unknown spring constant k. It is compressed to a distance \[\left( \frac{x}{2} \right)\] from its equilibrium position and released from rest. After approaching half the distance from equilibrium position, it hits another block and comes to rest momentarily, while the other block moves with a velocity\[3m{{s}^{-1}}\]. The total initial energy of the spring is

    A) \[0.3\text{ }J\]

    B) \[0.6\text{ }J\]

    C) \[0.8\text{ }J\]

    D) \[1.5\text{ }J\]

    Correct Answer: B

    Solution :

    [b] Applying momentum conservation \[{{\operatorname{m}}_{1}}{{u}_{1}} + {{m}_{2}}{{u}_{2}} = {{\operatorname{m}}_{1}}{{v}_{1}} + {{m}_{2}}{{v}_{2}}\] \[0.1u+m\left( 0 \right)= 0.1\left( 0 \right) +m\left( 3 \right)\] \[0.1\text{ }u=3\text{ }m\] \[\frac{1}{2}0.1{{u}^{2}}=\frac{1}{2}m{{\left( 3 \right)}^{2}}\] Solving we get, \[u=3\] \[\frac{1}{2}k{{x}^{2}}=\frac{1}{2}K{{\left( \frac{x}{2} \right)}^{2}}+\frac{1}{2}\left( 0.1 \right){{3}^{2}}\] \[\Rightarrow \,\,\,\,\,\frac{3}{4}k{{x}^{2}}=0.9\,\,\Rightarrow \,\,\,\frac{3}{2}\times \frac{1}{2}k{{x}^{2}}=0.9\] \[\therefore \,\,\,\,\,\,\,\,\frac{1}{2}K{{x}^{2}}= 0.6 J\] (total initial energy of the spring)


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