2. Questions Bank
  3. 9th Class
  4. Science
  5. Work and energy

9th Class Science Work and energy Question Bank Work, Energy and Power

  • question_answer
    A ball of mass \[2\,\,kg\] and another of mass \[4\,\,kg\] are dropped together from a \[60\] feet tall building. What will be the ratio of their kinetic energies after a fall of \[30\] feet?

    A) \[\sqrt{2}:1\]     

    B)        \[1:4\]

    C) \[1:2\]                 

    D)        \[1:\sqrt{2}\]

    Correct Answer: C

    Solution :

    \[{{m}_{1}}=2\,\,kg\]             \[{{m}_{2}}=4\,\,kg;\,\,{{h}_{1}}=60\,\,ft;\,\,{{h}_{2}}=30\,\,ft\] According to the law of conservation of energy,\[\Delta \,\,K.E.=\Delta \,\,P.E.\] \[\therefore \]      \[\frac{K.E{{.}_{1}}}{K.E{{.}_{2}}}=\frac{{{m}_{1}}g({{h}_{1}}-{{h}_{2}})}{{{m}_{2}}g({{h}_{1}}-{{h}_{2}})}=\frac{2\,\,kg(60-30)}{4\,\,kg(60-30)}\]           \[=\frac{2}{4}=1:2\]


You need to login to perform this action.
You will be redirected in 3 sec spinner