9th Class Science Time and Motion Question Bank Motion Summative Subjective Problems

  • question_answer
    A carrom board (\[\text{4ft}\times \text{4ft}\]square) has the queen at the centre. The queen, hit by the striker moves to the front edge, rebounds and goes in the hole being the striking line. (i) What is the magnitude of displacement of the queen from the centre to the front edge? (ii) find the magnitude of the displacement of the queen from the front edge to the hole (iii) from the centre to the hole

    Answer:

    Let ABCD be the carom board of\[4ft\times 4ft\]dimensions. ‘O’ is the centre where initially Queen is placed.
    Let E be the point on front edge where the Queen strikes and rebounds to fall in hole at A. Displacement of the Queen, (i) Displacement from centre to hole (OA) = ? From figure, \[OA=\frac{AC}{2}\] \[AC=\sqrt{A{{B}^{2}}+B{{C}^{2}}}=\sqrt{{{4}^{2}}+{{4}^{2}}}\,\,or\,\,4\sqrt{2}\]c \[\Rightarrow OA=2\sqrt{2}ft\] (ii) from centre to front edge = OE = ? Let F be the midpoint of CD. Join of (2ft). Let FE be x. or \[DE=(2-x)\] we can find OE, only if we know \[x.\] In right angled \[\Delta OEF,\] \[OE=\sqrt{{{2}^{2}}+{{x}^{2}}}\]                                                              ….(1) Lets try to find x. Let \[\angle EOF\,\,to\,\,\theta \] Draw a \[\bot EG\] at E such that \[\angle OEF=\angle GEO=\theta \] \[20=u+\frac{a}{2}(2-1)\] \[(\because n=1\,s)\]                                 \[20=u+\frac{a}{2}\]Alternate angles) In \[\Rightarrow \angle EAD,tan\theta =\frac{x}{2}\]                      ………..(1) \[\Rightarrow \angle AED,tan\theta =\frac{2-x}{4}\]                       …………..(2) From (1) and (2) \[\frac{x}{2}=\frac{2-x}{4}\,\,or\,\,6x=4\,\,or\,\,x=\frac{2}{3}\] Substituting the x value in (1), we get \[OE=\sqrt{{{2}^{2}}+{{\left( \frac{2}{3} \right)}^{2}}}\] \[\Rightarrow \sqrt{\frac{40}{9}}=\frac{2}{3}\sqrt{10}ft\] (iii) Displacement from front edge to hole (EA) = ? from \[\Delta AED\] \[EA\sqrt{{{(2-x)}^{2}}+{{4}^{2}}}\] \[=\sqrt{{{(2-\frac{2}{3})}^{2}}+{{4}^{2}}}\]                         \[\left( \because x=\frac{2}{3} \right)\] \[=\sqrt{{{\left( \frac{4}{3} \right)}^{2}}+{{4}^{2}}}=\frac{4}{3}\sqrt{10}ft\]


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