NCERT Solutions for Class 9 Science Chapter 7 – Motion

Motion is one of the most fundamental concepts in physics that describes the change in position of an object with respect to time. In our daily life, everything around us—from moving vehicles to flying birds—exhibits motion.

This chapter helps students understand key concepts such as distance, displacement, speed, velocity, and acceleration. It also introduces graphical representations like distance-time and speed-time graphs, which make it easier to analyze motion. Understanding motion lays the foundation for advanced topics in physics and helps in solving real-life problems related to movement and forces.

NCERT Solutions for Class 9 Science Chapter 7 – Motion (Q&A)

Q1. The speed-time graph for a car is shown.

(a) Find how far the car travels in the first 4 seconds.
(b) Which part of the graph represents uniform motion?

Ans:
(a) The distance travelled is equal to the area under the speed-time graph.
Distance travelled in first 4 seconds = area of shaded region = 12 cm (as per graph scale)

(b) The portion of the graph from 6 seconds to 10 seconds represents uniform motion, as the speed remains constant in this interval.

Q2. State which of the following situations are possible and give examples:

(a) An object with constant acceleration but zero velocity

Ans: Yes, it is possible.
Example: A ball thrown upwards has zero velocity at its highest point, but acceleration due to gravity is still acting on it.

(b) An object moving with acceleration but with uniform speed

Ans: Yes, it is possible.
Example: A vehicle moving in a circular path has constant speed but continuously changing direction, hence it has acceleration.

(c) An object moving in a direction with acceleration perpendicular to its direction

Ans: Yes, it is possible.
Example: In circular motion, acceleration acts towards the center, which is perpendicular to the direction of motion.

FAQs

Q1. What is motion in physics?

Motion is the change in position of an object with respect to time and a reference point.

Q2. What is the difference between distance and displacement?

• Distance is the total path travelled by an object.
• Displacement is the shortest distance between initial and final positions.

Q3. What is speed?

Speed is the distance travelled by an object per unit time.

Q4. What is velocity?

Velocity is the speed of an object in a specific direction.

Q5. What is acceleration?

Acceleration is the rate of change of velocity with respect to time.

Q6. What is uniform motion?

Uniform motion is when an object covers equal distances in equal intervals of time.

Q7. Why are graphs important in motion?

Graphs like distance-time and speed-time graphs help in visualizing and analyzing motion easily.