chapter 2 physics class 7D

 

A. Multiple Choice Questions

1. A motor van is running on a flyover. Its motion is

   • (c) circular
     Incorrect. The correct answer is (a) rectilinear (since a flyover is typically straight, the motion is along a straight path).

2. A stone falls freely from a cliff. Its motion is

   • (a) translatory
     Correct. Free-fall motion is rectilinear translatory motion (a type of translatory motion).

3. If equal distances are travelled by an object in equal intervals of time, its motion is said to be

   • (a) uniform
     Correct.

4. The SI unit of speed is

   • (b) m/s
     Correct.

5. Distance covered by a moving object in a unit time is called

   • (c) speed
     Correct.

6. Reeta runs through a distance of 10 km in 40 minutes. Her average speed is

   • (b) 15 km/h
     
     

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B. Assertion-Reason Questions

1. Assertion: Speedometer of a car measures the instantaneous speed of the car.
   Reason: Average speed is equal to the total distance covered by an object divided by the total time taken.

   • (a) Both Assertion [A] and Reason [R] are true.
     Correct. The speedometer measures instantaneous speed, and the reason is a correct definition of average speed.

2. Assertion: Displacement of an object can be either positive, negative, or zero.
   Reason: Displacement has both magnitude and direction.

   • (a) Both Assertion [A] and Reason [R] are true.
     Correct. Displacement is a vector quantity and can be positive, negative, or zero depending on direction.

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C. Fill in the blanks with suitable words

1. Rest and motion are relative terms.
2. Motion of the moon around the earth is an example of circular motion.
3. In rotatory motion, an object moves about a fixed axis.
4. A simple pendulum executes oscillatory motion.
5. A periodic motion is that which repeats itself again and again after a fixed interval of time.
6. Motion of a car on a city road is generally nonuniform.
7. The SI unit of speed is m/s.
8. Weight is measured in the unit kgf.

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D. State whether the following statements are true or false. If false, rewrite the correct form of statements.

1. An object travelling along a curved path is said to have rectilinear motion.

   • False. The correct statement: An object travelling along a curved path is said to have curvilinear motion.

2. A car moving around a circular park is said to be in translatory motion.

   • False. The correct statement: A car moving around a circular park is said to be in circular motion.

3. Motion of the earth about its own axis is a rotatory motion.

   • True.

4. A housefly flying in a filthy place is an example of random motion.

   • True.

5. The actual length of a path travelled is called the distance covered.

   • True.

6. Weight of an object is equal to its mass.

   • False. The correct statement: Weight of an object is the force of gravity acting on it and depends on the acceleration due to gravity (W = mg).

7. Motion of a pendulum clock is a periodic motion.

   • True.

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E. Define the following terms

1. Random motion

   • Motion in which an object has no specific path and frequently changes its direction or type of motion (e.g., a flying mosquito or a housefly).

2. Distance covered

   • The actual length of the path traveled by a moving object, regardless of direction.

3. Average speed

   • The ratio of the total distance traveled by an object to the total time taken. Formula: $\text{Average speed} = \frac{\text{Total distance}}{\text{Total time}}$.

4. Uniform motion

• Motion in which an object covers equal distances in equal intervals of time.

F. Differentiate Between the Following

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1. Rest and Motion

Rest vs. Motion

Aspect	Rest	Motion
Definition	An object is at rest if its position does not change with time relative to its surroundings.	An object is in motion if its position changes with time relative to its surroundings.
Example	A parked car, a building, or a book on a table.	A moving bus, a flying bird, or a rolling ball.
Relative Nature	Rest is a relative term. An object at rest relative to one reference point may be in motion relative to another.	Motion is also a relative term. An object in motion relative to one reference point may be at rest relative to another.
Energy	An object at rest has potential energy but no kinetic energy.	An object in motion has kinetic energy due to its movement.
Forces	If an object is at rest, the net force acting on it is zero (balanced forces).	If an object is in motion, a net force may or may not be acting on it (unbalanced forces cause acceleration).

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2. Rectilinear and Curvilinear Motion

Rectilinear vs. Curvilinear Motion

Aspect	Rectilinear Motion	Curvilinear Motion
Definition	Motion along a straight path.	Motion along a curved path.
Path	Straight line.	Curved line.
Example	A car moving on a straight road, a freely falling stone, or a ball rolling in a straight line.	A football kicked by a player, a cricket ball hit by a batsman, or a cyclist taking a turn.
Nature	Simplest form of translatory motion.	More complex than rectilinear motion.
Direction	Direction remains constant.	Direction changes continuously.

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3. Periodic and Nonperiodic Motion

Periodic vs. Nonperiodic Motion

Aspect	Periodic Motion	Nonperiodic Motion
Definition	Motion that repeats itself after a fixed interval of time.	Motion that does not repeat itself after a fixed interval of time.
Example	Motion of a pendulum, motion of the hands of a clock, or the Earth revolving around the Sun.	Motion of a car on a busy road, a football player running on the field, or a rolling cricket ball.
Repetition	Repeats at regular intervals.	Does not repeat at regular intervals.
Predictability	Highly predictable due to regular repetition.	Less predictable due to irregularity.

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4. Uniform and Nonuniform Motion

Uniform vs. Nonuniform Motion

Aspect	Uniform Motion	Nonuniform Motion
Definition	Motion in which an object covers equal distances in equal intervals of time.	Motion in which an object covers unequal distances in equal intervals of time.
Speed	Constant speed.	Variable speed.
Example	A car moving at a constant speed on a straight road or a train moving at a steady speed.	A car moving on a busy road with varying speed or a freely falling object.
Graph	Straight line on a distance-time graph.	Curved or zigzag line on a distance-time graph.
Acceleration	Zero acceleration (constant velocity).	Non-zero acceleration (changing velocity).

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5. Mass and Weight

Mass vs. Weight

Aspect	Mass	Weight
Definition	Mass is the quantity of matter present in an object.	Weight is the force with which the Earth attracts an object toward its center.
Nature	Scalar quantity (only magnitude).	Vector quantity (magnitude and direction).
SI Unit	Kilogram (kg).	Newton (N) or kilogram-force (kgf).
Measurement	Measured using a beam balance or physical balance.	Measured using a spring balance.
Dependence	Mass is constant and does not change with location.	Weight varies with the acceleration due to gravity (g), which changes with location.
Example	A 10 kg object has a mass of 10 kg on Earth, the Moon, or anywhere in the universe.	A 10 kg object weighs ~98 N on Earth (W = mg, where g ≈ 9.8 m/s²) but only ~16.3 N on the Moon (g ≈ 1.62 m/s²).
Zero Condition	Mass of an object can never be zero.	Weight of an object can be zero in a gravity-free environment (e.g., outer space).

G. Match the Columns

Column A	Column B
1. John running along a straight road	(e) Rectilinear motion
2. A cycle taking a turn on the road	(c) Curvilinear motion
3. Motion of a simple pendulum	(a) Oscillatory motion
4. A spinning charkha	(f) Rotatory motion
5. Motion of a guitar string	(b) Vibratory motion
6. Motion of smoke particles	(d) Random motion

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H. Encircle the Odd One Out and Give Reasons

1. Flowing water, blowing wind, a kite in flight, clock tower, running car

   • Odd one out: Clock tower
   • Reason: The clock tower is typically at rest (unless referring to its hands, which are in motion). The others involve objects in motion.

2. A spinning top, an electric fan in motion, a running train, a roulette wheel

   • Odd one out: Running train
   • Reason: The running train exhibits translatory motion, while the others exhibit rotatory motion.

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I. Give One Word for the Following

1. Motion that repeats itself again and again after a fixed interval of time → Periodic motion
2. Motion in which an object moves to and fro about its mean position → Oscillatory motion
3. Motion in which an object as a whole moves along a given path and different parts of the object cover equal distances → Translatory motion
4. Motion in which speed of a moving object remains constant → Uniform motion
5. The force with which the earth attracts an object → Weight
6. The distance covered by an object in unit time → Speed

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J. State the Type of Motion Performed by the Following

1. A girl swinging on a swing → Oscillatory motion
2. Vibrating string of a sitar → Vibratory motion
3. A drilling machine → Rotatory motion (if referring to the drill bit) and Translatory motion (if referring to the movement of the machine itself)

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K. Answer These Questions

1. Name three different types of motion. Give one example of each type.

   • Translatory motion: A car moving on a straight road.
   • Rotatory motion: A spinning top.
   • Oscillatory motion: A swinging pendulum.

2. Explain translatory motion.

   • Translatory motion is the motion in which an object moves as a whole along a straight or curved path, and all parts of the object cover equal distances in the same time.
   • Example: A ball rolling on the ground.

3. Give suitable examples to show that oscillatory motion is always periodic.

   • Oscillatory motion involves to-and-fro movement about a mean position. Examples:
     • A simple pendulum (swings back and forth at regular intervals).
     • The needle of a sewing machine (moves up and down repeatedly).
   • These motions repeat at fixed intervals, making them periodic.

4. What is rotatory motion? Give some examples.

   • Rotatory motion is the motion in which an object rotates about a fixed axis.
   • Examples:
     • A spinning top.
     • The blades of an electric fan.
     • A merry-go-round.

5. What do you mean by multiple motion?

   • Multiple motion (or complex motion) is when an object exhibits a combination of two or more types of motion simultaneously.
   • Example: A rolling wheel exhibits both rotatory motion (spinning) and translatory motion (moving forward).

6. Look around yourself and give three examples of motion which are repetitive in nature but are nonperiodic.

   • Motion of a rolling cricket ball on the ground.
   • Swinging of arms while walking.
   • Motion of lungs while breathing.

7. Define speed of a moving object and give its SI unit.

   • Speed is the distance covered by a moving object in unit time.
   • SI unit: Meter per second (m/s).

8. What do you mean by the weight of an object? Does weight of an object remain constant under all conditions?

   • Weight is the force with which the earth attracts an object toward its center (W = mg, where m is mass and g is acceleration due to gravity).
   • No, the weight of an object does not remain constant. It varies with the value of g (acceleration due to gravity), which changes from place to place (e.g., weight is less on the moon than on Earth).

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