Force and Motion — Exercise Solutions
Use this page alongside the official Samacheer Kalvi textbook. Solve every exercise question on your own first, then check the solutions below.
I. Multiple Choice Questions (MCQs)
Q1. Unit of speed is
- (a) m
- (b) s
- (c) kg
- (d) m/s
Speed = distance / time. Since distance is measured in metres (m) and time in seconds (s), the SI unit of speed is metre per second (m/s).
Q2. Oscillatory motion among the following is
- (a) Rotation of the earth about its axis
- (b) Revolution of the moon about the earth
- (c) To and fro movement of a vibrating string
- (d) All of these
Oscillatory motion is a to-and-fro movement about a fixed point. A vibrating string moves back and forth about its mean position, which is the textbook definition of oscillatory motion.
Q3. The correct relation among the following is
- (a) Speed = distance × time
- (b) Speed = distance / time
- (c) Speed = time / distance
- (d) Speed = 1 / (distance × time)
Speed is defined as the distance travelled per unit time. The formula is Speed = Distance / Time.
Q4. Gita rides with a speed of 40 km/hr for 40 minutes. Statement 1: Her speed is 1 km/minute. Statement 2: Her speed is 1 km/hour.
- (a) Statement 1 alone is correct
- (b) Statement 2 alone is correct
- (c) Both statements are correct
- (d) Neither statement is correct
Speed = 40 km / 40 minutes = 1 km/minute. Converting to km/hour: 1 km/minute = 60 km/hour, which is not 1 km/hour. So only Statement 1 is correct.
II. True or False (Correct the False Statements)
Q1. To and fro motion is called oscillatory motion.
Oscillatory motion is defined as the to-and-fro movement of an object about a fixed point (mean position).
Q2. Vibratory motion and rotatory motion are periodic motions.
Correction: Vibratory motion and oscillatory motion are periodic motions. Rotatory motion may or may not be periodic depending on whether it repeats at equal intervals.
Q3. Vehicles moving with varying speeds are said to be in uniform motion.
Correction: Vehicles with varying speeds are in non-uniform motion. Uniform motion means equal distances in equal intervals of time (constant speed).
Q4. Robots will replace humans in the future.
Correction: Robots will assist humans but cannot replace them completely. Robots perform repetitive and dangerous tasks, but human intelligence, creativity, and decision-making remain irreplaceable.
III. Fill in the Blanks
Q1. A bike moving on a straight road is an example of ______ motion.
When an object moves along a straight path, its motion is called linear or rectilinear motion.
Q2. Gravitational force is a ______ force.
Gravitational force acts between objects even without physical contact. It is a non-contact (or action-at-a-distance) force.
Q3. The motion of a potter's wheel is an example of ______ motion.
A potter's wheel rotates about its own fixed axis, which is the definition of rotatory motion.
Q4. When an object covers equal distances in equal intervals of time, it is in ______ motion.
Uniform motion means the object travels equal distances in every equal time interval — its speed remains constant.
IV. Match the Following
| No. | Column A | Column B | |
|---|---|---|---|
| 1 | Linear motion | a | A spinning top |
| 2 | Circular motion | b | Swing |
| 3 | Oscillatory motion | c | A bike on a straight road |
| 4 | Rotatory motion | d | Swirling a stone tied to a string |
| 5 | Curvilinear motion | e | Throwing a ball |
- 1 → c (Linear motion — A bike on a straight road)
- 2 → d (Circular motion — Swirling a stone tied to a string)
- 3 → b (Oscillatory motion — Swing)
- 4 → a (Rotatory motion — A spinning top)
- 5 → e (Curvilinear motion — Throwing a ball)
Linear motion follows a straight path. Circular motion follows a circular path. Oscillatory motion is to-and-fro about a mean position. Rotatory motion is movement about a fixed axis. Curvilinear motion follows a curved (non-circular) path.
V. Analogy
Q1. Kicking a ball : Contact force :: Falling of a leaf : ______?
Kicking involves physical contact (contact force). A leaf falls due to gravitational pull, which acts without physical contact (non-contact force).
Q2. Distance : metre :: Speed : ______?
The SI unit of distance is metre (m). The SI unit of speed is metre per second (m/s), since speed = distance / time.
Q3. Rotatory motion : A spinning top :: Oscillatory motion : ______?
A spinning top rotates about its own axis (rotatory). A pendulum swings to and fro about its mean position (oscillatory).
VI. Data Table — Uniform Speed Calculation
An elephant moves across a forest with uniform speed. Based on the formula Speed = Distance / Time, complete the table.
| Time (minutes) | Distance (km) |
|---|---|
| 4 | 8 |
| 8 | 16 |
| 12 | ? |
Given speed is uniform:
- Speed = Distance / Time = 8 km / 4 min = 2 km/min
At 12 minutes:
- Distance = Speed × Time = 2 × 12 = 24 km
Since the motion is uniform, speed stays constant at 2 km/min. In 12 minutes, the elephant covers 24 km.
VII. Web Chart — Classification of Motion
Complete the classification of motion types:
- Based on path: Linear, Curvilinear, Circular, Rotatory, Oscillatory, Zigzag (Irregular)
- Based on duration: Periodic, Non-periodic
- Based on speed: Uniform, Non-uniform
Motion can be classified by path (straight, curved, circular, rotational, oscillatory, zigzag), by duration (whether it repeats at equal intervals or not), and by speed (constant or varying).
VIII. One Word for the Following
Q1. Force acting without physical contact with the object.
Non-contact forces such as gravity and magnetic force act at a distance without touching the object.
Q2. Change in position of an object with time.
Motion is defined as a change in the position of an object with respect to time.
Q3. Motion that repeats itself after a fixed interval of time.
When a motion repeats at regular, equal intervals of time, it is called periodic motion (e.g., revolution of the moon).
Q4. Object travels equal distances in equal intervals of time.
In uniform motion, the speed remains constant and the object covers equal distances in every equal time interval.
Q5. Machine capable of carrying out a complex series of actions automatically.
A robot is an automatic machine that can perform complex tasks, especially those that are repetitive or dangerous for humans.
IX. Short Answer Questions
Q1. Define force.
Q2. Name different types of motion based on the path.
1. Linear motion — movement along a straight line (e.g., a bike on a straight road) 2. Curvilinear motion — movement along a curved path (e.g., a ball thrown in the air) 3. Circular motion — movement along a circular path (e.g., a stone tied to a string) 4. Rotatory motion — movement about a fixed axis (e.g., a spinning top) 5. Oscillatory motion — to-and-fro movement about a mean position (e.g., a pendulum) 6. Zigzag / Irregular motion — random, unpredictable path (e.g., a bee buzzing)
Q3. You are sitting in a moving car. Are you at rest or in motion with respect to your friend sitting next to you?
Motion is relative — it depends on the observer's frame of reference.
Q4. Rotation of the earth is a periodic motion — justify.
Q5. Differentiate rotational motion and curvilinear motion.
| Feature | Rotational Motion | Curvilinear Motion |
|---|---|---|
| Path | Moves about its own axis | Moves along a curved path |
| Fixed point | Rotates around a fixed axis | No fixed axis of rotation |
| Example | A spinning top, a potter's wheel | A ball thrown in the air |
X. Numerical Calculation
Q1. A vehicle covers 400 km in 5 hours. Calculate its average speed.
Speed = Distance / Time = 400 km / 5 h = 80 km/h
Average speed is total distance divided by total time taken.
XI. Detailed Answer Questions
Q1. What is motion? Classify different types of motion with examples.
Classification based on path:
1. Linear (Rectilinear) motion — object moves in a straight line. Example: a train on a straight track, a bike on a straight road. 2. Curvilinear motion — object moves along a curved path. Example: a ball thrown into the air at an angle. 3. Circular motion — object moves along a circular path. Example: a stone tied to a string and swirled. 4. Rotatory motion — object rotates about its own axis. Example: a spinning top, the earth rotating about its axis. 5. Oscillatory motion — object moves to and fro about a mean position. Example: a pendulum swinging, a vibrating string. 6. Zigzag / Irregular motion — object moves in a random, unpredictable path. Example: a housefly buzzing around a room.
Classification based on duration:
- Periodic motion — repeats at equal intervals of time. Example: revolution of the moon around the earth.
- Non-periodic motion — does not repeat at equal intervals. Example: a swinging cradle that slows down.
Classification based on speed:
- Uniform motion — equal distances covered in equal intervals of time. Example: a train moving at constant speed.
- Non-uniform motion — different distances covered in different intervals of time. Example: a bus starting, stopping, and accelerating in traffic.
XII. Fill in Examples — Motion Classification
Complete the classification table:
| Example | Type of Motion (by path) |
|---|---|
| Coconut falling from a tree | Linear |
| Heart beating | Oscillatory |
| Stone thrown into the air at an angle | Curvilinear |
| People walking in a bazaar | Zigzag / Irregular |
| A spinning top | Rotatory |
| Swirling a stone on a rope | Circular |
| A bike on a straight road | Linear |
| A pendulum | Oscillatory |
Additional Questions
Additional I. Multiple Choice Questions
AQ1. ______ is an ancient Indian astronomer.
- (a) C.V. Raman
- (b) Aryabhata
- (c) Usain Bolt
- (d) Edison
Aryabhata was an ancient Indian mathematician and astronomer who explained the rotation of the earth and calculated its circumference.
AQ2. Path of a housefly buzzing around the room is an example of:
- (a) Periodic motion
- (b) Non-periodic motion
- (c) Circular motion
- (d) None of these
A housefly moves in an unpredictable, irregular path — it does not repeat at fixed intervals, so it is non-periodic (zigzag/irregular) motion.
AQ3. Identify the periodic motion:
- (a) Horse racing in a field
- (b) Revolution of the moon around the earth
- (c) Coconut falling from a tree
- (d) Paper flight in the air
The moon revolves around the earth in a fixed orbit and repeats this motion at equal intervals (approximately 27.3 days), making it periodic motion.
AQ4. Cheetah's average speed is approximately:
- (a) 100 km/hr
- (b) 200 km/hr
- (c) 112 km/hr
- (d) 10 km/hr
The cheetah is the fastest land animal, with an average speed of about 112 km/h during short sprints.
AQ5. Robots scaled down to microscopic size are called:
- (a) Car robots
- (b) Home robots
- (c) Game robots
- (d) Nanobots
Nanobots are extremely small robots designed to operate at the microscopic scale, potentially inside the human body for medical procedures.
AQ6. The fastest land animal is:
- (a) Horse
- (b) Lion
- (c) Cheetah
- (d) Tiger
Additional II. True or False (Correct the False Statements)
AQ1. Motion occurs when an object is pulled or pushed by an agency.
Force (a push or pull) causes a change in the state of rest or motion of an object.
AQ2. Force executed by touching the body is called non-contact force.
Correction: Force executed by touching the body is called contact force. Non-contact forces act without physical contact (e.g., gravity, magnetism).
AQ3. Gravity pushes the ripened coconut from the tree to the ground.
Correction: Gravity pulls (not pushes) the ripened coconut down toward the earth. Gravity is always an attractive (pulling) force.
AQ4. Throwing a paper aeroplane is the best example of linear motion.
Correction: A paper aeroplane follows a curvilinear (curved) path, not a straight line. It is an example of curvilinear motion.
AQ5. Movement of a body about its own axis (like a spinning top) is linear motion.
Correction: Movement of a body about its own axis is rotatory motion, not linear motion. Linear motion is movement along a straight line.
AQ6. Motion repeated in equal intervals of time is called periodic motion.
By definition, periodic motion repeats itself at regular, equal intervals of time.
Additional III. Fill in the Blanks
AQ1. ______ are push or pull by an animate or inanimate agency.
AQ2. Application of force results in motion from a state of ______.
A force can change an object from a state of rest to a state of motion.
AQ3. Fast oscillations are referred to as ______.
When oscillations are very rapid (fast to-and-fro movement), they are called vibrations — for example, a vibrating phone or a plucked guitar string.
AQ4. Motion repeated in equal intervals of time is called ______.
AQ5. ______ are automatic machines.
Robots are machines that can carry out complex series of actions automatically, often programmed by computers.
AQ6. The term "Robot" comes from the tech word ______.
The word "robot" comes from the Czech word "robota," meaning forced labour or drudgery, introduced by Karel Capek in his 1920 play R.U.R.
AQ7. ______ is the study of robots in science.
Robotics is the branch of technology that deals with the design, construction, and operation of robots.
Additional IV. Short Answer Questions
AQ1. What is meant by the state of rest?
AQ2. What is a non-contact force?
AQ3. What is a contact force?
AQ4. What are the properties of force?
1. Force can change a body from a state of rest to a state of motion, or from motion to rest. 2. Force can change the direction of a moving object. 3. Force can change the speed of a moving object. 4. Force can change the shape or size of an object.
AQ5. A bus moves at 40 km/h. How much time will it take to cover 200 km?
Time = Distance / Speed = 200 km / 40 km/h = 5 hours
AQ6. Define average speed.
Average Speed = Total Distance / Total Time
AQ7. What are the types of motion based on speed?
1. Uniform motion — the object covers equal distances in equal intervals of time (constant speed). Example: a train moving at a steady 60 km/h. 2. Non-uniform motion — the object covers different distances in equal intervals of time (varying speed). Example: a bus in city traffic.
AQ8. Define uniform motion.
AQ9. Why are robots used in many places?
1. Perform mechanical and repetitive tasks faster and more accurately than humans. 2. Handle dangerous materials and work in hazardous environments. 3. Explore distant or inaccessible places like other planets or deep oceans. 4. Work continuously without fatigue or breaks.
AQ10. What are the important parts of a robot?
1. Electronic sensors — act as the robot's eyes and ears to perceive the environment. 2. Processing unit (brain) — analyses sensor data and makes decisions. 3. Actuators/motors — enable movement and action. 4. Power supply — provides energy for operation.
AQ11. What are nanobots?
AQ12. What are the future uses of robots?
1. Nanobots placed in the bloodstream could perform surgical procedures at the cellular level. 2. They could target and destroy cancer cells without harming healthy cells. 3. Robots could assist in disaster rescue, deep-sea exploration, and space missions. 4. Home robots could help with elderly care and daily household tasks.
Additional V. Detailed Answer Questions
AQ1. Classify the following motions by path:
1. Coconut falling from a tree — Linear motion (straight downward path) 2. Heart beating — Oscillatory motion (to-and-fro pumping action) 3. Stone thrown into the air at an angle — Curvilinear motion (curved parabolic path) 4. People walking in a bazaar — Zigzag / Irregular motion (random, unpredictable path) 5. Spinning top — Rotatory motion (rotates about its own axis)
AQ2. Classify the following motions by duration and speed:
| Example | Classification |
|---|---|
| Coconut falls to ground | Non-periodic (does not repeat at regular intervals) |
| Cart pulled by a bullock | Non-periodic (irregular, varying path) |
| Train journey | Non-uniform motion (speed varies — starts, stops, accelerates, decelerates) |
| Bouncing ball | Periodic motion (repeats at regular intervals as it bounces) |
| Revolution of the moon around the earth | Uniform periodic motion (constant speed, regular interval) |
Common Mistakes
Students often make these errors in exams. Avoid each one:
1. Confusing "push" and "pull" with contact vs. non-contact force. Pushing a door is a contact force, but gravity pulling a leaf is non-contact. The key distinction is physical touch, not the direction.
2. Saying gravity "pushes" objects down. Gravity always pulls (attracts) objects toward the earth. Never describe it as a push.
3. Mixing up rotatory and circular motion. Rotatory motion is about an object's own axis (e.g., a spinning top). Circular motion is along a circular path around an external centre (e.g., a stone on a string). They are different.
4. Calling a paper aeroplane an example of linear motion. A paper aeroplane follows a curved (curvilinear) path, not a straight line. Linear motion means a perfectly straight path.
5. Writing speed = distance × time. The correct formula is Speed = Distance / Time. Always remember: speed is distance divided by time.
6. Confusing periodic and non-periodic motion. Periodic motion repeats at equal time intervals (e.g., pendulum). Non-periodic motion does not repeat at regular intervals (e.g., a ball rolling to a stop).
7. Forgetting that motion is relative. A person sitting in a moving car is at rest relative to a fellow passenger but in motion relative to someone standing on the road. Always state your frame of reference.
Exam Checklist
Before your exam, make sure you can:
- [ ] Define force and list its effects (change of state, direction, shape, speed)
- [ ] Distinguish contact forces from non-contact forces with examples of each
- [ ] Classify motion by path (linear, curvilinear, circular, rotatory, oscillatory, zigzag)
- [ ] Classify motion by duration (periodic vs. non-periodic)
- [ ] Classify motion by speed (uniform vs. non-uniform)
- [ ] Write the formula Speed = Distance / Time and use it for calculations
- [ ] Convert units between m/s and km/h (multiply by 18/5 or 5/18)
- [ ] Identify the correct type of motion for any given real-world example
- [ ] Explain why gravity is a non-contact force
- [ ] Differentiate between rotatory and circular motion
- [ ] Describe oscillatory motion and give examples (pendulum, heartbeat, vibrating string)
- [ ] State properties of force and give at least two examples for each property
- [ ] Answer questions about robots, nanobots, and robotics briefly