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Political Science NCERT Solutions Class 9 Science Chapter 10 – Work and Energy
Class 9 Science
Last Updated: 15 April 2026
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Important Points
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Practice MCQ Questions (27 questions)
Q1. What is the unit of work in the SI system?
✓ Correct Answer: B
Q2. When is work said to be done on an object?
✓ Correct Answer: D
Q3. If the displacement is zero, what will be the work done?
✓ Correct Answer: A
Q4. What is the formula for work done when force and displacement are in the same direction?
✓ Correct Answer: B
Q5. What is the work done by a force of 10 N moving an object by 2 m?
✓ Correct Answer: B
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Frequently Asked Questions (FAQ)
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Tough Words (Glossary)
strenuous
Meaning: requiring great effort or energy
अर्थ: कड़ी मेहनत या अधिक ऊर्जा माँगने वाला
"Running a marathon is a strenuous activity."
parlance
Meaning: a particular way of speaking or using words
अर्थ: बोलने या शब्दों के उपयोग का खास तरीका
"In everyday parlance, we say we are 'working' even if no displacement happens."
displacement
Meaning: the shortest distance from the initial to the final position
अर्थ: प्रारंभिक से अंतिम स्थिति तक की सीधी दूरी (विस्थापन)
"No work is done if there is no displacement."
constant
Meaning: not changing; steady
अर्थ: स्थिर; जो बदलता नहीं
"A constant force acts on the object."
retarding
Meaning: slowing down or opposing motion
अर्थ: गति को धीमा करने या रोकने वाला
"A retarding force stops the trolley."
magnitude
Meaning: the size or amount of a quantity
अर्थ: मात्रा का परिमाण या आकार
"Work depends on the magnitude of force and displacement."
joule
Meaning: SI unit of work or energy
अर्थ: कार्य/ऊर्जा की एस.आई. इकाई (जूल)
"One joule is work done by a one-newton force through one metre."
newton
Meaning: SI unit of force
अर्थ: बल की एस.आई. इकाई (न्यूटन)
"A force of one newton moves the block slowly."
parallel
Meaning: in the same direction and never meeting
अर्थ: समांतर; एक ही दिशा में, कभी न मिलने वाले
"The baby pulls the car parallel to the ground."
perpendicular
Meaning: at a right angle (90°) to something
अर्थ: लंबवत; 90° कोण पर
"The force is perpendicular to the surface."
exert
Meaning: to apply (a force or effort)
अर्थ: लगाना (जैसे बल/प्रयास)
"We exert a force to lift the book."
expends
Meaning: uses up (energy or time)
अर्थ: खर्च करता है (ऊर्जा/समय)
"She expends a lot of energy while studying."
trolley
Meaning: a small cart on wheels
अर्थ: पहियों वाली छोटी गाड़ी (ट्रॉली)
"The girl pulls a trolley across the floor."
pebble
Meaning: a small smooth stone
अर्थ: कंकड़/छोटा चिकना पत्थर
"He pushed a pebble lying on the ground."
scientific
Meaning: based on or relating to science
अर्थ: वैज्ञानिक; विज्ञान से संबंधित
"The scientific definition of work needs displacement."
configuration
Meaning: arrangement or shape of parts
अर्थ: विन्यास; भागों की व्यवस्था/आकृति
"A spring stores energy due to its configuration."
mechanical energy
Meaning: energy due to motion and position (KE + PE)
अर्थ: यांत्रिक ऊर्जा (गतिज + स्थितिज)
"A swinging pendulum has mechanical energy."
kinetic energy
Meaning: energy possessed due to motion
अर्थ: गतिज ऊर्जा; गति के कारण ऊर्जा
"A rolling ball has kinetic energy."
potential energy
Meaning: energy stored due to position or shape
अर्थ: स्थितिज ऊर्जा; स्थिति/आकृति के कारण ऊर्जा
"Water stored high in a tank has potential energy."
gravitational
Meaning: related to the force of gravity
अर्थ: गुरुत्वाकर्षण से संबंधित
"The object gains gravitational potential energy when raised."
conservation
Meaning: keeping the total quantity unchanged
अर्थ: संरक्षण; कुल मात्रा का अपरिवर्तित रहना
"Energy conservation means total energy stays constant."
transformation
Meaning: change from one form to another
अर्थ: रूपांतरण; एक रूप से दूसरे में बदलना
"Potential energy transformation into kinetic energy occurs during fall."
velocity
Meaning: speed with direction
अर्थ: वेग; दिशा सहित गति
"The velocity of the car increased on the slope."
acceleration
Meaning: rate of change of velocity
अर्थ: त्वरण; वेग के परिवर्तन की दर
"The hammer gained acceleration as it fell."
uniform
Meaning: unchanging; constant throughout
अर्थ: समान/एकसमान; पूरे समय समान
"The body moved with uniform velocity."
rate
Meaning: how fast something happens per unit time
अर्थ: दर; प्रति इकाई समय में होने की गति
"Power is the rate of doing work."
work (physics)
Meaning: product of force and displacement in direction of force
अर्थ: कार्य; बल और उसी दिशा में विस्थापन का गुणनफल
"If displacement is zero, work is zero."
energy
Meaning: capacity to do work
अर्थ: ऊर्जा; कार्य करने की क्षमता
"We get energy from food to play and study."
power
Meaning: rate at which work is done or energy is transferred
अर्थ: शक्ति/पावर; कार्य होने या ऊर्जा स्थानांतरण की दर
"A powerful engine finishes the job quickly."
watt
Meaning: SI unit of power
अर्थ: शक्ति की एस.आई. इकाई (वाट)
"A 60-watt bulb uses 60 joules per second."
kilowatt
Meaning: one thousand watts
अर्थ: हज़ार वाट; किलोवाट
"The motor is rated at 2 kilowatts."
transfer
Meaning: to move from one place/object to another
अर्थ: स्थानांतरित करना; एक से दूसरे में ले जाना
"Energy can transfer from a moving hammer to a nail."
retains
Meaning: keeps or holds
अर्थ: संजोता/कायम रखता है
"The toy retains energy in its wound spring."
applied
Meaning: put to use; exerted
अर्थ: लागू किया गया; लगाया हुआ
"Work depends on the applied force."
withdrawn
Meaning: removed or taken back
अर्थ: हटाया/वापस लिया गया
"The balloon returns to shape when the force is withdrawn."
capability
Meaning: ability or power to do something
अर्थ: क्षमता; कुछ करने की योग्यता
"A raised hammer has the capability to do work."
hammer
Meaning: a tool with a heavy head used for hitting
अर्थ: हथौड़ा
"The hammer drives the nail into the wood."
elastic
Meaning: able to return to original shape after being stretched
अर्थ: लोचदार; खिंचने के बाद मूल आकार में आने वाला
"A rubber band is elastic and stores energy."
height
Meaning: how tall or how high above ground
अर्थ: ऊंचाई
"Lifting a book to a height increases its potential energy."
against (physics)
Meaning: opposing a force like gravity
अर्थ: के विरुद्ध (भौतिकी में), जैसे गुरुत्व के विरुद्ध
"Work is done against gravity when we lift objects."
expression (formula)
Meaning: a mathematical statement
अर्थ: गणितीय व्यंजक/सूत्र
"We derived an expression for kinetic energy."
derive
Meaning: to obtain from reasoning or calculation
अर्थ: व्युत्पन्न करना; गणना से निकालना
"Students derive the formula for power."
average
Meaning: total divided by number or time
अर्थ: औसत; कुल/समय से भाग
"Average power equals total work over total time."
unit (SI)
Meaning: standard measure used in science
अर्थ: इकाई (एस.आई.)
"Joule is the SI unit of energy."
positive work
Meaning: work done when force and displacement are in same direction
अर्थ: धनात्मक कार्य; जब बल व विस्थापन एक दिशा में हों
"Pulling the trolley forward does positive work."
negative work
Meaning: work done when force opposes displacement
अर्थ: ऋणात्मक कार्य; जब बल विस्थापन का विरोध करे
"Friction does negative work on moving objects."
friction
Meaning: force that opposes motion between surfaces
अर्थ: घर्षण; सतहों के बीच गति का विरोध करने वाला बल
"Friction reduces the speed of the cart."
resistance (air)
Meaning: opposition by air to motion
अर्थ: प्रतिरोध (वायु); गति का वायु द्वारा विरोध
"We ignored air resistance in the calculation."
store (energy)
Meaning: to keep energy for later use
अर्थ: ऊर्जा संचित करना
"A wound spring can store energy."
precise
Meaning: exact and accurate
अर्थ: सटीक
"In science, words have precise meanings."