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# Long Answers - Motion, Science, Class 9 Class 9 Notes | EduRev

## Class 9 : Long Answers - Motion, Science, Class 9 Class 9 Notes | EduRev

The document Long Answers - Motion, Science, Class 9 Class 9 Notes | EduRev is a part of the Class 9 Course Class 9 Science by VP Classes.
All you need of Class 9 at this link: Class 9

Q1. (a) What is motion?
(b) State types of motion.
(c) Derive the unit for acceleration.
Ans.
(a) Motion: An object is said to be in motion when its position changes with time. We describe the location of an object by specifying a reference point. Motion is relative.
The total path covered by an object is said to be the distance travelled by it.

(b) There are two types of motion: Uniform motion and non-uniform motion.
Uniform motion: When an object covers equal distances in equal intervals of time, it is said to be in uniform motion.
Non-uniform motion: Motion where object cover unequal distances in equal intervals of time.

(c) Acceleration, ‘a’ is change in velocity per unit time.

a= (v-u) /t = (m/s) / s

∴      a = m/s2

Q2. (a) What is uniform circular motion?

(b) An athlete runs on a circular track, whose radius is 50 m with a constant speed. It takes 50 seconds to reach point B from starting point A. Find
(i) the distance covered
(ii) the displacement
(iii) the speed.
Ans.
(a) When a body moves in a circular path with uniform speed, its motion is called uniform circular motion.

(b) Radius = 50 m Time = 50 s

(i) The distance covered by an athlete A to B i.e., semicircle of the track
∴ circumference = 2πr
circumference-half = πr
= (22/7) × 50
distance = 157.14 m

(ii) Displacement from A − B is diameter AB
d = 2r
d = 2 × 50 = 100 m

(iii) Speed = ?

speed = distance/time = 157.14/50 = 3.143

∴ Speed = 3.143 m/s.

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