NCERT Question 8 - Chapter 8 Class 9 - Motion

Last updated at April 16, 2024 by

The speed-time graph for a car is shown is Fig. 8.12.

(a) Find how far does the car travel in the first 4 seconds. Shade the area on the graph that represents the distance travelled by the car during the period.
(b) Which part of the graph represents uniform motion of the car?

q 8.jpg

Answer

(b) Q8 (b).jpg

The part of the graph between time 6s to 10s represents uniform motion of the car

 

(a)

Q8 (a).jpg

In a velocity − time graph,

Distance = Area of v-t Graph

 

Here, we find approximate area using Area of Triangle

Distance = Area Δ OAB

    = 1/2 × b × h

    = 1/2 × 4 × 6

    = 12 m

 

But, this is an inaccurate method to find Area, since the red portion is

not covered

Slide4.JPG

Slide5.JPG

Q8 (c).jpg

∴ Total area = 15.2 + 0.8 + 0.4 + 0

= 16.4 sq units

 

Area under v − t graph gives distance

Hence, the distance covered by the car in 0−4 s = 16.4 m

 

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Transcript

Finding Area by Counting the Squares From the graph, We can see that On time axis, 5 squares = 2 units 1 square = 2/5 units On speed axis, 3 squares = 2 units 1 square = 2/3 units ∴ Area of each square = 2/5 × 2/3 = 4/15 sq units ∴ 1 square represents 4/15 m distance Now, we take Area of fully filled square = Area of 1 square = 4/15 Area of more than half square = Area of 1 square = 4/15 Area of half-filled square = 1/2 × Area of 1 square = 1/2 × 4/15 Area of less than half-filled square = 0 Area of less than half square = 0

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