CBSE – 9th Standard Science

Q1. What is motion?

Ans.  The movement of any object from its initial position is called motion.

Q2. What is origin?

Ans.  To describe the position of an object we need to specify a reference point called the origin.

Q3. What is Displacement?

Ans. The shortest distance measured from the initial to the final position of an object is known as the displacement.

Q4. Name two quantities that describe the overall motion of an object?

Ans. The distance and the displacement, are used to describe the overall motion of an object.

Q5. What is Uniform motion?

Ans. As the object covers equal distances in equal intervals of time, it is said to be in uniform motion.

Q6. What is Non Uniform motion?

Ans. When objects cover unequal distances in equal intervals of time, is said to be in non uniform motion.

Q7. What is Speed?

Ans. It is the rate of motion of an object to find out the distance travelled by the object in unit time.

Q8. What is the S.I unit of speed?

Ans. The SI unit of speed is metre per second. This is represented by the symbol  m/s.

Q9. How to calculate the average speed of an object?

Ans. The average speed of an object is obtained by dividing the total distance travelled by the total time taken.

Q10. What is velocity?

Ans. The rate of motion of an object can be more comprehensive if we specify its direction of motion along with its  speed. The quantity that specifies both these aspects is called velocity.

Q11. What is Acceleration?

Ans. Acceleration, is a measure of the change in the velocity of an object per unit time.

Q12. What is the S.I unit of acceleration?

Ans. The SI unit of acceleration is m/s^-2.

Q13. Give an example of uniformly accelerated motion?

Ans. The motion of a freely falling body is an example of uniformly accelerated motion.

Q14. Give an example of uniformly accelerated motion?

Ans. If a car travelling along a straight road increases its speed by unequal amounts in equal intervals of time, then the car is said to be moving with non-uniform acceleration.

Q15. Which graph is used to describe the motion of an object?

Ans. To describe the motion of an object, we can use line graphs.

Q16. What do you mean by equation of motion?

Ans. To relate an objects movement in a uniform acceleration like its velocity, acceleration during motion and the distance covered by it in a certain time interval by a set of equations known as the equations of motion.

Q17. Write three equations of motion?

Ans. (i) v = u + at

(ii) s = ut + 1/2 at²

(iii) 2 a s = v² – u²

Q18. What ‘a’,‘s’, ‘u’ ,’v’, and ‘t’ means in an equation of motion?

Ans. In the equation of motion ‘u’ is the initial velocity of the object which moves with uniform acceleration ‘a’ for time ‘t’, ‘v’ is the final velocity, and ‘s’ is the distance travelled by the object in time ‘t’.

TRY THESE :-

Q.1  An object travels 16 m in 4 s and then another 16 m in 2 s. What is

        the average speed of the object?

Q.2  Usha swims in a 90 m long pool. She covers 180 m in one minute

        by swimming from one end to the other and back along the same straight path.

        Find the average speed and average velocity of Usha.

Q.3  The odometer of a car reads 2000 km at the start of a trip and

        2400 km at the end of the trip. If the trip took 8 h, calculate the average

        speed of the car in km h–1 and m s–1

Q.4  A train starting from rest attains a velocity of 72 km h–1 in

        5 minutes. Assuming that the acceleration is uniform, find (i) the

        acceleration and (ii) the distance travelled by the train for attaining this velocity

Q.5  The brakes applied to a car produce an acceleration of 6 m s-2 in

         the opposite direction to the motion. If the car takes 2 s to stop after the

        application of brakes, calculate the distance it travels during this time