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Motion — Science STD 9 — Question

CBSE BoardEnglish MediumSTD 9ScienceMotion3 Marks
Question
Fig shows the distance-time graph of three objects A, B and C. Study the graph and answer the following questions:


  1. Which of the three is travelling the fastest?
  2. Are all three ever at the same point on the road?
  3. How far has C travelled when B passes A?
  4. How far has B travelled by the time it passes C?
✓

Answer

  1. Object B
  2. No
  3. 5.714km
  4. 5.143km
  1. Speed $=\frac{\text{Distance}}{\text{Time}}$
Slope of graph $=\frac{\text{y-axis}}{\text{x-axis}}=\frac{\text{Distance}}{\text{Time}}$Therefore, Speed = slope of the graph.
Since slope of object B is greater than objects A and C, it is travelling the fastest.
  1. All three objects A, B and C never meet at a single point. Thus, they were never at the same point on road.

7 square box = 4km$\therefore$ 1 square box $=\frac{4}{7}\text{km}$C is 4 blocks away from origin therefore initial distance of C from origin Distance of C from origin when B passes A = 8kmThus, Distance travelled by C when B passes A$= 8 - \frac{16}{7 }$$=\frac{(56 - 16)}{7 }$​​​​​​​$=\frac{40}{7}= 5.714\text{km}$


  1. Distance travelled by B by the time it passes C = 9 square boxes
$9×\frac{4}{7} =\frac{36}{7}= 5.143\text{km}$

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