9th Class Science Time and Motion Question Bank 9th CBSE Science Motion

  • question_answer
          With the help of a graph, derive the relation v = u + at.

    Answer:

                       Consider the velocity-time graph of an object that moves under uniform acceleration as shown in the figure . From this graph, we can see that initial velocity of the object (at point A) is u and then it increases to v (at point B) in time t. The velocity changes at a uniform rate a. As shown in the figure, the lines BC and BE are drawn from point B on the time and the velocity axes respectively, so that the initial velocity is represented by OA, the final velocity is represented by BC and the time interval t is represented by OC. BD = BC - CD, represents the change in velocity in time interval t. If we draw AD parallel to OC, we observe that BC = BD + DC = BD + OA       Substituting, EC with v and OA with u, we get         V=BD + u Or              BD = v ? u                                   ?? (1) Thus from the given velocity-time graph, the acceleration of the object is given by Substiuting, OC with t, we get or BD = at                      ?..(2)


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