Check NCERT based important extra questions & answers of CBSE Class 9 Science (Chapter 8 Motion). These questions and answers are important for the preparation of the upcoming CBSE Class 9 Science Exam 2020-21. These questions can be asked in the exam with slight modifications.
CBSE Class 9 Science Exam 2020-21: NCERT Based Important Extra Questions (With Answers) Chapter 8 - Motion
Question: In which of the following cases of motions, the distance moved and the magnitude of displacement are equal?
(a) A boy is moving on a straight road
(b) A bicycle is moving in circular path
(c) The earth is revolving around the Sun
(d) The pendulum is moving to and fro
Answer:
(a) A boy is moving on a straight road.
CBSE Class 9 Revised Syllabus for 2020-2021
Question: What is the slope of a velocity – time graph gives?
Answer: The slope of a velocity – time graph gives acceleration.
Question: The displacement of a moving ball in a given interval of time is zero.
Would the distance travelled by the object also be zero? Justify your answer.
Answer:
No because it might be possible that the moving object returns to its initial position. So the distance travelled is not zero.
Question: The numerical ratio of displacement to distance for a moving object is
(a) always less than one
(b) always equal to one
(c) always more than one
(d) equal or less than one
Answer:
(d) equal or less than one.
As, Distance ≥ Displacement.
Question: A ball starting from rest travels 20 m in the first 2 s and 160 m in next 4 s. What will be the velocity after 7 s from the start.
Answer:
s1 = ut + (½) at2 or 20 = 0 + (½) a (2)2 or a = 10 m s–2
v = u + at = 0 + (10 × 2) = 20 m s–1
s2 = 160 = vt′ + (½) a’ (t’)2 = (20 × 4) + (½) a’ x 16 ⇒ a’ = 10 m s–2
As acceleration is the same, we have v′ = 0 + (10 × 7) = 70 m s–1
Question: What is uniform circular motion?
Answer: If an object moves in a circular path with uniform speed, its
motion is called uniform circular motion.
Question: Fill in the blanks
The __________ of an object is the distance covered per unit time, and ______ is the displacement per unit time.
Answer:
The speed of an object is the distance covered per unit time, and velocity is the displacement per unit time.
Question: Draw a velocity versus time graph of a stone thrown vertically upwards and then coming downwards after attaining the maximum height.
Answer:
https://www.jagranjosh.com/imported/images/E/Articles/CBSE-9th-Science-Exam-2020-21-ch-8-answer-18.jpg
Question: Obtain a relation for the distance travelled by an object moving with a
uniform acceleration in the interval between 4th and 5th seconds.
Answer:
Using the equation of motion, s = ut + (½) at2
Distance travelled in 5 s, s = u × 5 + (½) a x 52 or s = 5 u + (25/2)a ....(i)
Similarly, distance travelled in 4 s, s′ = 4 u + (16/2) a …..(ii)
Distance travelled in the interval between 4th and 5th second = (s – s′) = [u + (9/2) a] unit.
Question: A particle is moving in a circular path of radius r. The displacement after traversing a complete circle would be:
(a) Zero
(b) π r
(c) 2 r
(d) 2π r
Answer:
(a) Zero.
NCERT Solutions for Class 9 Maths: Download chapter-wise solutions in PDF
