NCERT Class-9 Science Solutions: Chapter 8-Motion Part 4

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Question 17:

The velocity-time graph (Fig.) shows the motion of a cyclist. Find

  1. Its acceleration

  2. Its velocity and

  3. The distance covered by the cyclist in 15 seconds.

Image velocity-time graph Q 17

Image Velocity-Time Graph Q 17

Image velocity-time graph Q 17

Answer:

  1. Since velocity is not changing, acceleration is equal to zero.

  2. Reading the graph,

  3. Distance covered in

Image velocity-time graph

Image Velocity-Time Graph

Image velocity-time graph

Question 18:

Draw a velocity versus time graph of a stone thrown vertically upwards and then coming downwards after attaining the maximum height.

Answer:

Image velocity versus time graph

Image Velocity Versus Time Graph

Image velocity versus time graph

Long Answer Questions

Question 19:

An object is dropped from rest at a height of and simultaneously another object is dropped from rest at a height . What is the difference in their heights after if both the objects drop with same accelerations? How does the difference in heights vary with time?

Answer:

Initial difference in height

Distance travelled by first body in 2 s

Distance travelled by another body in 2 s

After 2 s, height at which the first body will be

After 2 s, height at which the second body will be

Thus, after 2 s, difference in height

Initial difference in height

Thus, difference in height does not vary with time.