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9th Class Science Force and laws of motion Question Bank Force and Laws of Motion

  • question_answer
    A ball of mass 0-1 kg is thrown against a wall. It strikes the wall normally with a velocity of 30 \[\text{m}{{\text{s}}^{\text{-1}}}\]and rebounds from there with a velocity of 20\[\text{m}{{\text{s}}^{\text{-1}}}\]. The impulse of the force exerted by the ball on the wall is

    A)  0.5 Ns           

    B)         50 Ns

    C)  5 Ns                       

    D)         1 Ns

    Correct Answer: C

    Solution :

     Impulse \[=\] force\[\times \]time\[=\]change in momentum\[=mv-mu=0.1(-20-30)=-5\] Since units in all the options are same, we need not bother to think about the units. Also since there is no fight of plus or minus sign in the options, we will give the correct answer as\[5\,\,Ns\]. Note that the direction of initial velocity is considered as positive and that of the final velocity is considered as negative.


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