# NCERT Class 9 Science Solutions: Chapter 8 – Motion Part 3

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Question 2:

Q. A bus decreases its speed from 80 km to 60 km in 5 s. Find the acceleration of the bus.

**Answer:**

Initial speed of the bus,

Final speed of the bus,

Time take to decrease the speed,

Acceleration,

Here, the negative sign of acceleration indicates that the velocity of the car is decreasing.

Question 3:

Q. A train starting from a railway station and moving with uniform acceleration attains a speed 40 km in 10 minutes. Find its acceleration.

**Answer:**

Initial velocity of the train,(Since the train is initially at rest)

Final velocity of the train

Time taken,

Hence, the acceleration of the train is

Question 1:

Q. What is the nature of the distance-time graphs for uniform and non-uniform motion of an object?

**Answer:**

The distance-time graph for uniform motion of an object is a straight line (as shown in the following figure).

The distance-time graph for non-uniform motion of an object is a curved line (as shown in the given figure).

Question 2:

Q. what can you say about the motion of an object whose distance-time graph is a straight line parallel to the time axis?

**Answer:**

When an object is at rest, its distance-time graph is a straight line parallel to the time axis.

A straight line parallel to the x-axis in a distance—time graph indicates that with a change in time, there is no change in the position of the object. Thus, the object is at rest.

Question 3:

Q. what can you say about the motion of an object if its speed-time graph is a straight line parallel to the axis?

**Answer:**

Object is moving uniformly.

A straight line parallel to the time axis in a speed-time graph indicates that with a change in time, there is no change in the speed of the object. This indicates the uniform motion of the object.