NCERT Solutions for Class 9 Science Chapter 7 Work Energy and Simple Machines provide clear, step-by-step answers to every exercise and in-text question from the chapter Work Energy and Simple Machines of the NCERT textbook Exploration. Prepared by subject experts as per the latest NCERT (CBSE) syllabus for 2026-27, these NCERT Solutions for Class 9 Science help you understand each concept, write exam-ready answers, and check your own solutions. You can read them online below or download the free Class 9 Science Chapter 7 question-answer PDF.
NCERT Solutions for Class 9 Science Chapter 7 Work Energy and Simple Machines
- Class: Class 9
- Subject: Science
- Chapter: Chapter 7 – Work Energy and Simple Machines
- Textbook: Exploration (NCERT)
- Study material: NCERT Solutions – questions with answers, free PDF
These solutions answer all the exercise questions of Chapter 7 Work Energy and Simple Machines — including the in-text questions, short-answer and long-answer questions, and activities — with complete explanations so you can follow the method, not just the final answer. Read the full solutions below.
NCERT Solutions Class 9 Science Chapter 7 Work Energy and Simple Machines View Download
NCERT Solutions for Class 9 Science Chapter 7 PDF Download
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Questions Covered in This Chapter
These NCERT Solutions answer all 47 questions of this chapter. The questions solved are:
- What will be the magnitude of velocity of the child at the bottom of the blue slide?
- Will two children of different masses reach the bottom of the same slide with the same velocity?
- Which of the slides will result in the largest magnitude of velocity for the child at its bottom?
- But when forces change with time or act in complicated ways, applying these laws directly can become difficult. Is there a simpler and more powerful way to understand such situations?
- In the previous chapter, a weightlifter is shown holding a barbell steady in her hands (Fig. 6.8). Is she doing any work on the barbell while holding it steady?
- Is the work done by friction on the stack of coins that travels on a rough surface (Fig. 6.13c) — positive, negative or zero?
- We have seen that when a force is applied and an object is displaced, work is done on it. Does this cause the object to gain capacity to do further work?
- When you pedal a bicycle on a flat road, your muscles supply energy. In what forms does this muscular energy appear as you ride?
- How much is the energy possessed by an object by virtue of its motion?
- Two objects A and B of mass m and 4 m have the same kinetic energy. What is the ratio of the magnitude of velocities of A and B?
- Does the kinetic energy of an object which moves with constant velocity change with its position?
- Raise the ball over the sand bed to a height of about 1 m and drop it (Fig. 7.17). Is a depression created in the sand? Why does the ball create a depression?
- Now, raise the ball to the height of 2 m and release it at a slightly different position over the sand bed such that the depressions do not overlap. Repeat this step one more time. Compare the depths of the depressions. Is there any difference? In which case is the depression deepest and in which case the shallowest?
- Does the potential energy of an object near the surface of the Earth change if it moves with constant velocity in the horizontal direction? What if the object is gradually raised in the vertical direction?
- Take the bob to one side to a point P, which is at the level of the horizontal line and let it go. Observe it at the extreme points of the first couple of oscillations. Does the bob almost reach the level of the horizontal line?
- For the situation depicted in Fig. 7.19, calculate the mechanical energy of the ball just before it hits the ground and show that even at this position, it is mgh.
- You may have seen an exhibit like that in Fig. 7.22 in a science park, where a ball is released from the highest point. Describe how the kinetic energy and potential energy change at points A, B and C. Why do subsequent points, such as C, D and E, usually have lower heights compared to the previous ones? Could it have anything to do with the energy lost due to friction?
- You can place the box on a smooth inclined plank as shown in (Fig. 7.26b), and push the box up the plank to the platform. Does this method require a smaller force?
- Next, place the plank against the top of the pile of books or stool as shown in Fig. 7.27a. Pull the cart along the plank slowly and steadily. Is the reading of the spring balance (the force required) smaller than that of step 2?
- Now, reduce the angle between the plank and the base as shown in Fig. 7.27b, and repeat the step 3. Observe how the force required changes as the plank becomes less steep.
- Explain why roads on hills are built to wind around in gentle slopes rather than going straight up (Fig. 4.26)?
- To reach a higher floor, we find climbing an inclined ladder easier in comparison to climbing a vertical ladder (Fig. 7.30). Explain why.
- On the other end of the scale, place one eraser. Does the stapler lift up? If not, add one more eraser.
- By applying a small force at one end of the lever, a larger force can be applied on the object on the other end of the lever. How is this possible?
- Record all observations and measurements, and complete the Table 7.1 by adding more rows. [Number of coins in the left pan, n₁ (Effort); Distance of left pan from the fulcrum, L₁ (cm); Number of coins in right pan, n₂ (Load); Distance of right pan from the fulcrum, L₂ (cm)]
- Why is it easier to open the lid of a can by using a spoon as shown in Fig. 7.35?
- Why do you push an object closer to scissors fulcrum when you want to cut an object which is hard?
- Throughout history, many designs of perpetual machines (using wheels, weights or magnets) have been proposed but none actually work. Why do all real machines eventually slow down and stop? Explain in terms of work and energy.
- … it were possible to build a perpetual motion machine, which once started, could continue doing useful work forever, without any fuel or electricity?
- State whether True or False. (i) Work is said to be done when a force is applied, even if the object does not move. (ii) Lifting a bucket vertically upward results in positive work done on the bucket. (iii) The SI unit for both work and energy is joule (J). (iv) A motionless stretched rubber band has kinetic energy. (v) Energy can change from one form to another.
- Fill in the blanks. (i) Work done = ______ × ______ (in the direction of force). (ii) 1 joule of work is done when a force of ______ newton displaces an object by 1 metre in the direction of the force. (iii) The expression for kinetic energy of a body of mass m and velocity v is ______. (iv) The potential energy of an object of mass m at a small height h from the Earth’s surface is ______. (v) Power is defined as the ______ at which work is done.
- When a ball thrown upwards reaches its highest point, tick which of the following statement(s) are correct? (i) The force acting on the ball is zero. (ii) The acceleration of the ball is zero. (iii) Its kinetic energy is zero. (iv) Its potential energy is maximum.
- For each of the following situations, identify the energy transformation that takes place: (i) a truck moving uphill, (ii) unwinding of a watch spring, (iii) photosynthesis in green leaves, (iv) water flowing from a dam, (v) burning of a matchstick, (vi) explosion of a fire cracker, (vii) speaking into a microphone, (viii) a glowing electric bulb, and (ix) a solar panel.
- A student is slowly lifted straight up in an elevator from the ground level to the top floor of a building. Later, the same student climbs the staircase, all the way to the top. Given that the height of the building is h = 72.5 m, acceleration due to gravity is g = 10 m s–2, and student’s mass is m = 50 kg. (i) Find the gain in the potential energy if the student is lifted straight up to the top. (ii) Find the gain in the potential energy when the student climbs the stairs to the same top. (iii) What do you conclude about the dependence of the potential energy on the path taken?
- A crane lifts a mass m to the 10th floor of a building in a certain time. It then raises the same mass to the 20th floor of the same building in double the time. How much more energy and power are required? Assume that the height of all floors is equal.
- Which factors determine the energy required to raise a flag from the ground to the top of a tall flagpole using a pulley? Does raising the flag slowly or quickly change the amount of work done? If the speed at which the flag is raised is doubled, how does the power requirement change? Explain your answers.
- A man of mass 60 kg rides a scooter of mass 100 kg. He accelerates the scooter to a velocity v. The next day, his son with a mass of 40 kg joins him as a passenger. If the scooter reaches the same speed on both days in the same time interval, what is the ratio of the fuel of the tank used on the two days? Assume that the energy transfer to the scooter happens entirely due to fuel, and no other losses occur due to air resistance and friction.
- On a seesaw with sliding seats, a child is sitting on one side and an adult on the other side. The adult weighs twice that of the child. The seesaw however is balanced. Draw a figure which depicts this situation showing the distances from the fulcrum where the child and the adult are seated.
- A ball of mass 2 kg is thrown up with a velocity of 20 m s–1. (i) Identify the sign of the work done by gravity on the ball during its upward motion and its downward motion. (ii) If the ball reaches a height of 19.4 m, how much work was done by air resistance (assume g = 10 m s–2).
- A 10.0 kg block is moving on horizontal floor with negligible friction. As shown in the Fig. 7.37, a variable force is applied on the block in its direction of motion from its position at 0 m till 4 m. If the block had a kinetic energy of 180 J when it was at 0 m, find the block’s speed (i) at 0 m, and (ii) at 4 m. Does the block have negative acceleration in any portion of its motion?
- The gravitational attraction on the surface of the Moon (lunar surface) is about 1/6th of that on the surface of the Earth. An astronaut can throw a ball up to a height of 8 m from the surface of the Earth. How far up will the ball thrown with the same upward velocity travel from the surface of the Moon?
- A 1000 kg car is moving along a road at a constant speed. Suddenly, the driver notices some obstruction ahead and applies the brakes to come to a complete stop. The graphical representation of motion of the car starting from the instant the driver spots the traffic ahead is shown in Fig. 7.38. (i) Describe how the car moves between positions A and B. (ii) Calculate the kinetic energy of the car at A. (iii) State the work done by the brakes in bringing the car to a halt between B and C. (iv) What does the kinetic energy of the car transform into?
- The potential energy-displacement graph of a 0.5 kg ball moving along a frictionless track is shown in Fig. 7.39. At O, the velocity of the ball is 0 m s–1 and potential energy is 30 J. Calculate the velocity of the ball at P, Q and R.
- A coconut of mass 1.5 kg falls from the top of a coconut tree onto the wet sand on a beach. The height of the tree is 10 m. On impact, the coconut comes to rest by making a depression in the sand. (i) Calculate the velocity of the coconut just before it hits the sand. (ii) Assume that the average resistive force of sand is 3000 N and all of the coconut’s energy is used to create the depression in the sand. Calculate the depth of the depression the coconut makes in the sand. Assume g = 10 m s–2.
- Remove both the ends from a pen so that the refill can slide freely through the barrel (Fig. 7.40). Fix the pen cap to the side of the barrel and attach a rubber band to the clip of the cap. Connect the free end of the rubber band to the refill using a safety pin. Stretch and release the rubber band. The refill shoots out, showing the conversion of elastic potential energy into kinetic energy. Repeat with different amounts of stretch, and observe how the distance travelled changes. Is there a relationship between the stretch and the distance travelled?
- Construct one or more simple machines, or a combination of them (lever, pulley, and inclined plane) using easily available materials, such as cardboard, wooden strips or rulers, pencils or bolts (to act as a fulcrum), thread or rope, small pulleys (or two bottle caps stuck together), and paper cups to hold small weights. Be imaginative in your design. Use your model to lift or move a small load, measure the effort and the load, and calculate the mechanical advantage.
- Computer simulations can help in visualising physical quantities that are difficult to observe directly. The PhET simulations (https://phet.colorado.edu) provide interactive models, such as Energy Skate Park, Energy Forms and Changes, Pendulum Lab, and Masses and Springs. Use these to explore how different forms of energy change as parameters, such as mass, height, and friction are varied.
Chapter at a Glance
- Work done by a constant force = force × displacement in the direction of the force, W = F × s. Its SI unit is the joule: 1 J = 1 N × 1 m = 1 kg m 2 s –2 . Work is zero when F = 0, when s = 0, or when the force is perpendicular to the displacement.
- Work is positive when the displacement is along the force and negative when it opposes the force. Work has no direction — only a sign. For a force that varies, the work done is the area under the force–displacement graph .
- Work–energy theorem: work done on an object (or system) = change in its energy. This holds even when the forces are not constant, and it is the tool that gives every other formula in the chapter.
- Kinetic energy K = ½mv 2 — the energy of motion. Gravitational potential energy U = mgh near the Earth's surface — the energy of position. Both are measured in joules.
- Conservation of mechanical energy: for an object moving only under gravity, K + U stays constant. A falling body at height h′ has mgh′ + ½mg 2 t 2 = mgh at every instant.
- Power is the rate of doing work, P = W/t. 1 watt = 1 joule per second; 1 horsepower = 746 W. The same work done in half the time needs twice the power.
- Simple machines — pulley, inclined plane, lever — change the size or direction of the force you must apply. Mechanical advantage = load / effort. A machine never reduces the total work: if the force falls, the distance rises in the same proportion.
How to Download NCERT Solutions for Class 9 Science Chapter 7 PDF
Follow these simple steps to get the Work Energy and Simple Machines questions-and-answers PDF from Exploration.
- Search NCERT Solutions for Class 9 Science Chapter 7 aglasem and open this page.
- Read the exercise questions with answers for Work Energy and Simple Machines shown above.
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NCERT Solutions for Class 9 Science – All Chapters
There are more chapters to study besides Work Energy and Simple Machines in Science. Here are the NCERT Solutions for all chapters of Class 9 Science.
- Chapter 1 Exploration Entering the World of Secondary Science
- Chapter 2 Cell the Building Block of Life
- Chapter 3 Tissues in Action
- Chapter 4 Describing Motion Around Us
- Chapter 5 Exploring Mixtures and Their Separation
- Chapter 6 How Forces Affect Motion
- Chapter 7 Work Energy and Simple Machines
- Chapter 8 Journey Inside the Atom
- Chapter 9 Atomic Foundations of Matter
- Chapter 10 Sound Waves Characteristics and Applications
- Chapter 11 Reproduction How Life Continues
- Chapter 12 Patterns in Life Diversity and Classification
- Chapter 13 Earth As a System Energy Matter and Life
NCERT Solutions for Class 9 – All Subjects
Just like Chapter 7 of Science, you can get the exercise questions with answers for every other subject of Class 9. Here are the NCERT Solutions for all subjects of Class 9.
NCERT Solutions for Class 9 Science Chapter 7 – An Overview
The key highlights of this study material are as follows.
| Aspects | Details |
|---|---|
| Class | Class 9 |
| Subject | Science |
| Chapter Number | Chapter 7 |
| Chapter Name | Work Energy and Simple Machines |
| Book Name | Exploration |
| Book By | NCERT (National Council of Educational Research and Training) |
| Educational Resource Here | NCERT Solutions of Class 9 Science Chapter 7 for all exercises |
| More Questions Answers of This Subject | NCERT Solutions for Class 9 Science |
| Download Book Chapter | NCERT Book Class 9 Science |
| All Questions Answers For This Class | NCERT Solutions for Class 9 |
| Complete Solutions | NCERT Solutions |
NCERT Solutions for Class 9 Science Chapter 7 Work Energy and Simple Machines – FAQs
What are the NCERT Solutions for Class 9 Science Chapter 7 Work Energy and Simple Machines?
They are the complete, step-by-step answers to all the exercise and in-text questions of Chapter 7 Work Energy and Simple Machines from the NCERT Class 9 Science textbook Exploration, written by experts as per the latest NCERT syllabus.
How can I download the Class 9 Science Chapter 7 solutions PDF for free?
Open this page on aglasem, read the Work Energy and Simple Machines questions with answers, and click the “Download Solutions PDF” link. The Class 9 Science Chapter 7 NCERT Solutions PDF is completely free to download.
Are these NCERT Solutions as per the latest 2026-27 syllabus?
Yes. The NCERT Solutions for Class 9 Science Chapter 7 are based on the latest NCERT textbook Exploration and the current 2026-27 CBSE syllabus, so the questions and answers match what you study in class.
Where can I get NCERT Solutions for the other chapters of Class 9 Science?
You can find the answers to every chapter on the NCERT Solutions for Class 9 Science page, and solutions for every subject on the NCERT Solutions for Class 9 page.
How do NCERT Solutions help in exam preparation?
They show the correct method to solve each question, help you write answers the way they are expected in exams, let you check and correct your own work, and save revision time — which together improve your marks in Class 9 Science.
If you have any queries on NCERT Solutions for Class 9 Science Chapter 7 Work Energy and Simple Machines, then please ask in the comments below.
