Topic outline

• Motion and Time

Q28. Explain how in ancient time a day, a month and a year were measured?

Ans. Our ancestors noticed that many events in nature repeat themselves after definite intervals of time. For example, they found that the sun rises every day in the morning. The time between one sunrise and the next was called a day. Similarly, a month was measured from one new moon to the next. A year was fixed as the time taken by the earth to complete one revolution of the sun.

Q29. What are the points that should be considered while choosing the most suitable scale for drawing a graph?

Ans. Some of the points to be kept in mind while choosing the most suitable scale for drawing a graph are:

i.        the difference between the highest and the lowest values of each quantity.

ii.        the intermediate values of each quantity, so that with the scale chosen it is convenient to mark the values on the graph, and

iii.        to utilise the maximum part of the paper on which the graph is to be drawn.

Q30. Write down the steps to draw a graph.

Ans. Steps

i.        Draw two perpendicular lines to represent the two axes and mark them as OX and OY.

ii.        Decide the quantity to be shown along the x-axis and that to be shown along the y-axis.

iii.        Choose a scale to represent the distance and another to represent the time on the graph.

iv.        Mark values for the time and the distance on the respective axes according to the scale you have chosen.

v.        Mark the points on the graph paper to represent each set of values for distance and time. Join the points.

Q31. Which of the following distance-time graphs shows a truck moving with speed which is not constant?

i.                                                    ii.

iii.                                          iv.

Ans.

Image from NCERT

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