NCERT Class-9 Science Solutions: Chapter 8-Motion Part 5

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Question 20:

An object starting from rest travels in first and in next . What will be the velocity after from the start?

Answer:

Since acceleration is the same, we have

Question 21:

Using following data, draw time - displacement graph for a moving object:

Time vs Displacement
Time vs displacement

Time (s)

0

2

4

6

8

10

12

14

16

Displacement (m)

0

2

4

4

4

6

4

2

0

Use this graph to find average velocity for first , for next and for last .

Answer:

Image time - displacement graph

Image Time - Displacement Graph

Image time - displacement graph

Average velocity for first 4 s.

For next 4 s

(or as x remains the same from 4 to 8 seconds, velocity is zero)

For last 6 s

Question 22:

An electron moving with a velocity of enters into a uniform electric field and acquires a uniform acceleration of in the direction of its initial motion.

  1. Calculate the time in which the electron would acquire a velocity double of its initial velocity.

  2. How much distance the electron would cover in this time?

Answer:

Given initial velocity

And acceleration

  1. Final velocity

    To find

  2. Using