Chapter 6 of 13

Questions Notes Flashcards Summary Formulas Quiz Concepts Syllabus Plan

Updated 6 August 2026

NCERT Solutions

How Forces Affect Motion

CBSE · Class 9 · Science

NCERT Solutions for How Forces Affect Motion — CBSE Class 9 Science.

110 questions72 flashcards5 concepts

Interactive on Super Tutor

Studying How Forces Affect Motion? Get the full interactive chapter.

Quizzes, flashcards, AI doubt-solver and a step-by-step study plan — built for ncert solutions and more.

Try Super Tutor — Free

1,000+ Class 9 students started this chapter today

A comparative diagram showing the different types of simple and compound epithelial tissues, including squamous, cuboidal, columnar, ciliated columnar, glandular, and stratified squamous epithelium, w — Learn better with visuals Super Tutor has hundreds of illustrations like this across every chapter — all free to try.
Get started

28 Questions Solved · 3 Sections

14 worked solutions below. Unlock all 28 free in Super Tutor

Think It Over

1Why does a canoe move forward when the canoeist pushes water backwards with their paddle and why does it move faster when they push harder?Show solution

When the canoeist pushes the water backwards, the water exerts an equal and opposite force on the paddle and canoe, pushing it forwards. This is an example of Newton’s third law of motion. If the canoeist pushes harder, the force on the water is larger, so the forward force on the canoe is larger too, and the canoe moves faster.

Not sure why a step works? check your working in Super Tutor

2Suppose the same canoeist uses the same paddle force in two different canoes, one empty and one carrying another passenger. In which case will the canoe move faster?Show solution

With the same paddle force, the canoe will move faster in the empty canoe because its mass is smaller. For the same force, a smaller mass gets a larger acceleration, so the empty canoe gains speed more quickly than the canoe carrying a passenger.

Not sure why a step works? check your working in Super Tutor

Pause and Ponder

1A weightlifter lifts a barbell (Fig. 6.8). List two forces that are acting on the barbell. Are these forces balanced if the weightlifter keeps the barbell steady?Show solution

Two forces acting on the barbell are:
- Gravitational force due to the Earth, acting downward.
- Upward force applied by the weightlifter’s hands.

If the weightlifter keeps the barbell steady, these forces are balanced because they are equal in magnitude and opposite in direction.

Not sure why a step works? check your working in Super Tutor

2Two players R and S are participating in an arm-wrestling match (Fig. 6.9). At the instant, when the arms tilt to the front direction (out of the page towards you), are the forces exerted by the players balanced? If not, which player exerted the larger force?Show solution

When the arms tilt towards the front direction, the net force is in that direction. So the forces are unbalanced. The player whose force is acting in the front direction is exerting the larger force. From the figure context, that is S.

Not sure why a step works? check your working in Super Tutor

3An object is moving with a constant velocity. Is there a net force acting upon it?Show solution

If an object is moving with constant velocity, its acceleration is zero. Therefore, the net force is zero by Newton’s first law.

Not sure why a step works? check your working in Super Tutor

4Suppose, no net force is acting on an object. Which of the following situations are possible?Show solution

If no net force acts on an object, then by Newton’s first law:
- an object remains at rest if it is at rest,
- an object continues with constant velocity if it is already moving.

A moving object with constant acceleration is not possible when net force is zero.

Not sure why a step works? check your working in Super Tutor

5In the real world, it is difficult to find a situation where no forces are acting on an object. But by applying additional forces, a condition can be achieved where the net force on the object is zero. Explain with the help of an example.Show solution

A condition of zero net force can be achieved by applying another force that cancels the first one. For example, when a person pushes a box on the floor, friction acts in the opposite direction. If the applied force equals the force of friction, the two forces are balanced, the net force becomes zero, and the box moves with constant velocity or remains at rest, depending on the situation.

Not sure why a step works? check your working in Super Tutor

6A toy car of mass

100\mathrm{g}

is moving with a constant velocity of

0.5\mathrm{ms}^{-1}

. What is the net force acting on the toy car?Show solution

A toy car moving with constant velocity has zero acceleration.

Using Newton’s second law,

F = ma = 0.1\,\text{kg} \times 0 = 0\,\text{N}

So the net force is zero.

Not sure why a step works? check your working in Super Tutor

7Two children of different masses are sitting on identical swings. To impart identical initial acceleration, for which child would you require to apply a larger force? Explain why.Show solution

To produce the same initial acceleration, a larger force is needed for the heavier child. By Newton’s second law,

F = ma

For the same acceleration, force is proportional to mass. So the child with greater mass requires a larger force.

Not sure why a step works? check your working in Super Tutor

8How are glass items packed for transportation using a bubble wrap or hay protected from damage?Show solution

Glass items are packed with bubble wrap or hay to increase the time of impact during shocks and collisions. When the stopping time increases, the acceleration becomes smaller, so the force on the glass is reduced. This protects the glass from breaking.

Not sure why a step works? check your working in Super Tutor

9Why does a fireperson sometimes struggle when holding the pipe issuing water?Show solution

A fireperson sometimes struggles because the water jet exerts an equal and opposite force on the pipe. This reaction force pushes back strongly on the fireperson, making the pipe hard to hold.

Not sure why a step works? check your working in Super Tutor

10Suppose a spacecraft is moving in a region of space where the gravitational force acting upon it is negligible. Suggest how can it change its velocity.Show solution

If gravitational force is negligible, the spacecraft can change its velocity by firing its engine and expelling gas. The exhaust gases push backward, and the spacecraft gets an equal and opposite force forward or backward depending on the direction of the exhaust, so its velocity changes.

Not sure why a step works? check your working in Super Tutor

Revise, Reflect, Refine

1Using a horizontal force

F

, a table is moved across the floor at a constant velocity. How much is the frictional force exerted by the floor on the table?Show solution

Since the table moves with constant velocity, the net force is zero. Therefore, the frictional force must be equal in magnitude to the applied force and opposite in direction.

So frictional force = F.

Not sure why a step works? check your working in Super Tutor

2For a ball moving on a smooth frictionless surface, choose the appropriate option that will make the following statements physically correct.Show solution

For a ball on a smooth frictionless surface:
- If no net force acts, the velocity remains the same.
- If a net force acts in the direction of motion, speed will increase.
- If a net force acts opposite to motion, speed will decrease.

Not sure why a step works? check your working in Super Tutor

3Two blocks P and Q on a smooth horizontal surface are shown in Fig. 6.36a and Fig. 6.36b. Two forces of magnitudes

4\mathrm{N}

and

5\mathrm{N}

are acting in opposite directions on block P, while block Q is moving with a constant velocity.

4While practising for the snake boat race (*Vallum kalli* in Kerala), 100 oarsmen are rowing a boat together. Out of these, 95 row backwards to propel the boat forward. But by mistake, 5 oarsmen row in the opposite direction. If each oarsman applies a horizontal force of 200 N, what is the net force on the snake boat? (Ignore drag forces, air friction, etc.)

5When a net force acts on an object, we observe that the object accelerates:

6The position-time graph for four objects A, B, C and D moving along a straight line are given in Fig. 6.37. A net force acts on:

7A sailor jumps out from a small boat to the shore (Fig. 6.38). As the sailor jumps forward, will the boat move? If yes, in which direction and why.

8During a high jump event, a landing mat or sand bed is placed for the athlete to fall upon (Fig. 6.39). Explain the reason behind it.

9A hand cart loaded with vegetables collides with an identical but empty hand cart. During the collision:

10The acceleration-mass graph for the acceleration produced by a force on objects of different masses is plotted in Fig. 6.40. Plot the force-mass graph for this case.

11The velocity-time graph of an object of mass

10\mathrm{kg}

moving along a straight line is shown in Fig. 6.41. Calculate the force acting on the object by using the graph.

12A bullet of mass

50\mathrm{g}

moving with a speed of

100\mathrm{ms}^{-1}

enters a heavy stationary wooden block and stops after penetrating a distance of

50~\mathrm{cm}

. Estimate the stopping force acting on the bullet (assume that the bullet undergoes constant acceleration within the block).

13An ace footballer converted a penalty shot by kicking the football with a speed of

108\mathrm{km}\mathrm{h}^{-1}

. The estimated force they imparted was

800\mathrm{N}

. The mass of the football was

0.4\mathrm{kg}

. Calculate the time of contact between their foot and the ball.

14An object of mass

2\mathrm{kg}

moving with a constant velocity of

10\mathrm{ms}^{-1}

encounters a rough patch where the force of friction on the object is

7\mathrm{N}

. At the same time, an additional constant force of

3\mathrm{N}

opposing the motion is applied on the object. After entering the rough patch, how much distance does the object travel before coming to rest?

15A tractor pulls a harrow (a ploughing tool) of mass

m_{1}

with a net force

F

resulting in an acceleration of

a_{1}

. The same tractor pulls a trolley of mass

m_{2}

with a force

F

producing an acceleration of

a_{2}

. If the tractor now pulls the trolley with the harrow placed on it (with the same force

F

), then obtain an expression for the resulting acceleration in terms of

a_{1}

and

a_{2}

. Ignore friction.

16When the pole of a bar magnet is brought close to a magnetic compass, the bar magnet and the compass needle (which is also a magnet) exert a magnetic force on each other. As per Newton's third law of motion, both the forces are equal in magnitude and opposite in direction. However, the compass needle moves, whereas the bar magnet does not move (Fig. 6.42). Explain why.

14 more solved questions in How Forces Affect Motion

Every remaining exercise is solved step by step in Super Tutor, plus practice quizzes and flashcards for this chapter. Free to start.

Stuck on a step?

Ask Super Tutor AI to explain any solution on this page in a simpler way — free, 24x7.

Ask a Doubt Free

Frequently Asked Questions

What are the important topics in How Forces Affect Motion for CBSE Class 9 Science?

Key topics in How Forces Affect Motion include Classification of Plant Tissues, Classification of Plant Tissues, Complete Classification of Plant and Animal Tissues. These are the concepts CBSE Class 9 examiners draw on most — study them first, then practise related questions.

How to score full marks in How Forces Affect Motion — CBSE Class 9 Science?

Understand the core concepts first, then work through the 110 practice questions available for this chapter. Revise formulas and definitions regularly, and use flashcards for quick recall before the exam.

Where can I get free NCERT Solutions for How Forces Affect Motion Class 9 Science?

This page has free step-by-step NCERT Solutions for every exercise question in How Forces Affect Motion (CBSE Class 9 Science) — written the way examiners award marks: given, formula, working, answer.

Sources & Official References

Content is aligned to the official syllabus. Refer to the board website for the latest curriculum.

More resources for How Forces Affect Motion

All 13 chapters — CBSE Class 9 Science NCERT Solutions

For serious students

Get the full How Forces Affect Motion chapter — for free.

Quizzes, flashcards, AI doubt-solver and a step-by-step study plan for CBSE Class 9 Science.

Try Super Tutor Free

Try the full chapter — Free

How Forces Affect Motion

Studying How Forces Affect Motion? Get the full interactive chapter.

Think It Over

Pause and Ponder

Revise, Reflect, Refine

Frequently Asked Questions

Sources & Official References

More resources for How Forces Affect Motion

Practice Quiz

Important Questions

Revision Notes

Formula Sheet

Chapter Summary

Concept Maps

Study Plan

Flashcards

Syllabus

Get the full How Forces Affect Motion chapter — for free.