TALEEM: KINEMATICS OF LINEAR MOTION Chapter # 03 Physics 10th

Physics 10th - Question Answers

KINEMATICS OF LINEAR MOTION
Chapter # 03

Q.1: Define rest?

Ans: REST:
A body is said to be in the state of rest if it does not change its position with respect to its surroundings.

Q.2: Define motion? Write down its types?

Ans: MOTION:
A body is said to be in the state of motion if it changes its position with respect to its surroundings.

TYPES OF MOTION:
There are many types of motion, but the common types are given below:

Translatory Or Linear Motion:
When a body moves on a straight path and the direction of the motion remains constant during its motion; its motion is called translatory or linear motion.
Examples:
- Motion of a boat
- Motion of a car
Rotatory Motion:
When a body spins or rotates about a fixed point or axis, its motion is called rotatory motion.
Examples:
- Motion of the earth about its axis
- Motion of the blades of an electric fan
Vibratory Or Oscillatory Motion:
When a body moves to and fro about its mean position, its motion is called vibratory or oscillatory motion.
Examples:

Motion of a swing
Motion of the pendulum of a clock

Q.3: Define kinematics, mechanics, and dynamics?

Ans: KINEMATICS:
The word kinematics is derived from the Greek word ‘kinema’ meaning motion. The branch of physics that deals with the motion of objects without any reference to the force or agent causing the motion is called kinematics.

MECHANICS:
Mechanics is the branch of physics that deals with the kinematics and dynamics of objects.

DYNAMICS:
The word dynamics is taken from a Greek word ‘dynamic’ meaning power. So, dynamics is the branch of physics which deals with the causes of motion and how they affect the motion.

Q.4: Define scalar and vector quantities with examples?

Ans: SCALAR QUANTITIES:
Physical quantities, which are completely specified by their magnitude only, are called scalar quantities. Scalar quantities can be added, subtracted, and multiplied by simple arithmetic methods.

Example:
Mass, time, distance, speed, work, energy, temperature, charge, etc.

VECTOR QUANTITIES:
Physical quantities, which are completely specified by their magnitude and direction both, are known as vector quantities.

Example:
Displacement, velocity, acceleration, force, weight, torque, momentum, etc.

Q.5: What are the differences between distance and displacement?

Ans: DIFFERENCE BETWEEN DISTANCE AND DISPLACEMENT:

Distance	Displacement
It is the horizontal measurement between two points.	It is the minimum distance covered in a particular direction.
It is a scalar quantity.	It is a vector quantity.
It only needs magnitude for specification.	It needs not only magnitude but also direction for specification.
It is denoted by S.	It is denoted by d.

Q.6: Define speed? Write down its formula and unit?

Ans: SPEED:
The distance covered by a moving body in a unit time is called speed. It is denoted by $v$ . It is a scalar quantity.

Formula:

$Speed = \frac{Distance}{Time}$ $v = \frac{S}{t}$

Unit Of Speed:
The S.I. unit of speed is $\frac{m}{s}$ or $m s^{- 1}$ .

Q.7: Write down the types of speed?

Ans: TYPES OF SPEED:
There are the following types of speed:

Uniform Speed:
If a moving body covers equal distance in equal intervals of time, the speed of the body is called uniform speed.
Variable Speed:
If a moving body does not cover equal distance in equal intervals of time, its speed is called variable speed.
Average Speed:
If we divide the distance covered by a moving body by the time interval, then we get average speed.

$Average speed = \frac{Total Distance}{Total Time}$ $V_{a v} = \frac{S}{t}$

Q.8: Define velocity? Write down its formula and unit?

Ans: VELOCITY:
The distance covered by the body in a particular direction is called velocity.

Formula:

$Velocity = \frac{Displacement}{Time}$ $\vec{v} = \frac{\vec{d}}{t}$

Unit Of Velocity:
The SI unit of velocity is $\frac{m}{s}$ or $m s^{- 1}$ .

Q.9: Write down the types of velocity?

Ans: TYPES OF VELOCITY:
There are the following types of velocity:

Uniform Velocity:
When speed and direction of motion of a body do not change, the velocity is said to be uniform.
Variable Velocity:
The velocity of the body changes if either its speed changes, its direction changes, or both. Such a velocity is called variable velocity.
Average Velocity:
If we divide the total displacement covered by the moving body by the total time taken by the moving body, then we get average velocity.
Formula:
${\vec{V}}_{a v} = \frac{\vec{d}}{t}$

Q.10: What is acceleration? Write down its formula and unit?

Ans: ACCELERATION:
The rate of change of velocity is called acceleration. It is denoted by “ $a$ ”. It is a vector quantity.

Formula:

$Acceleration = \frac{Change of Velocity}{Time}$ $\vec{a} = \frac{\vec{v_{f}} - \vec{v_{i}}}{t} = \frac{Δ v}{Δ t}$

Unit Of Acceleration:
The S.I. unit of acceleration is $m / s^{2}$ or $m s^{- 2}$ .

Q.11: Write down the types of acceleration?

Ans: TYPES OF ACCELERATION:
There are the following types of acceleration:

Positive Acceleration:
If the velocity of a body increases continuously, then the acceleration is said to be positive or simple acceleration, and its direction is the same as that of the motion.
Negative Acceleration:
If the velocity of a body decreases continuously, then the acceleration is said to be negative and is called deceleration or retardation. Its direction is opposite to the direction of motion.
Uniform Acceleration:
If the velocity of a body changes by equal amount in equal intervals of time, then its acceleration is said to be uniform acceleration.
Variable Acceleration:
If the rate of change of velocity is variable, then the acceleration is said to be variable acceleration.
Zero Acceleration:
If a body moves with uniform velocity, then it has zero acceleration.
Average Acceleration:
The ratio between the total change in velocity and time is called average acceleration.
Formula:
$\vec{a} = \frac{\vec{v_{f}} - \vec{v_{i}}}{t} = \frac{Δ v}{Δ t}$

Q.12: What is the difference between speed and velocity?

Ans: DIFFERENCE BETWEEN SPEED AND VELOCITY:

Speed	Velocity
It is the ratio between distance and time.	It is the ratio between displacement and time.
It is a scalar quantity.	It is a vector quantity.
Mathematically:

$V = \frac{S}{t}$

| Mathematically:

$\vec{V} = \frac{\vec{d}}{t}$

Q.13: What are the differences between scalar and vector quantities?

Ans: DIFFERENCE BETWEEN SCALAR AND VECTOR QUANTITIES:

Scalar Quantity	Vector Quantities
The physical quantities which are completely specified by their magnitude only are called scalar quantities.	The physical quantities which are completely specified by their magnitude and direction both are called vector quantities.
Scalars can be added, subtracted, and multiplied by simple arithmetic methods.	They are added, subtracted, and multiplied by geometric or trigonometric methods.
Scalars can be represented by a number, e.g., 50 seconds.	A vector can be represented graphically by a line segment with an arrow.
Mass, volume, time, distance, speed, density, work, energy, temperature, charge, etc., are scalar quantities.	Area, displacement, velocity, acceleration, force, momentum, torque, etc., are vector quantities.

Q.14: Derive the first equation of motion?

Ans:
Suppose a body is moving with initial velocity “ $v_{i}$ ” and undergoes uniform acceleration “ $a$ ” for a time “ $t$ ”, such that its final velocity becomes “ $v_{f}$ ”.

Change in velocity of the body in time $t = v_{f} - v_{i}$ .

Therefore, change in velocity in unit time $t = \frac{(v_{f} - v_{i})}{t}$ .

As change in velocity in unit time (i.e., the rate of change of velocity) is called acceleration:

$a = \frac{v_{f} - v_{i}}{t}$

$v_{f} - v_{i} = a t$ $v_{f} = v_{i} + a t$

This is the first equation of motion.

Q.15: Derive the second equation of motion?

Ans:
Suppose a body starts with an initial velocity $v_{i}$ and travels with uniform acceleration “ $a$ ” for a period of time “ $t$ ”. The distance covered by the body in this time is “ $S$ ” and its final velocity becomes $v_{f}$ .

Since the acceleration is uniform, the velocity of the body increases or decreases by equal amounts in equal time intervals (i.e., the velocity changes at a constant rate).

Therefore:

$Average velocity = \frac{v_{f} + v_{i}}{2}$

Distance travelled = average velocity × time

$S = \frac{v_{f} + v_{i}}{2} \times t$

From the first equation of motion, we have:

$v_{f} = v_{i} + a t$ $S = [\frac{v_{i} + (v_{i} + a t)}{2}] \times t$ $S = \frac{v_{i} + v_{i} + a t}{2} \times t$ $S = \frac{2 v_{i} + a t}{2} \times t$ $S = \frac{2 v_{i} t + a t^{2}}{2}$ $S = v_{i} t + \frac{1}{2} a t^{2}$

This is the second equation of motion.

Q.16: Derive the third equation of motion?

As we know from the first equation of motion:

$v_{f} = v_{i} + a t$

Squaring both sides of the above equation, we have:

$(v_{f})^{2} = (v_{i} + a t)^{2}$

$v_{f}^{2} = v_{i}^{2} + 2 v_{i} a t + a^{2} t^{2}$

$v_{f}^{2} = v_{i}^{2} + 2 v_{i} a t + 2 (\frac{1}{2} a^{2} t^{2})$

$v_{f}^{2} = v_{i}^{2} + 2 a (v_{i} t + \frac{1}{2} a t^{2})$

But, we know that:

$S = v_{i} t + \frac{1}{2} a t^{2}$

So,

$v_{f}^{2} = v_{i}^{2} + 2 a (S)$

$v_{f}^{2} = v_{i}^{2} + 2 a S$

Hence,

$2 a S = v_{f}^{2} - v_{i}^{2}$

The above equation is the third equation of motion.

Q.17: What do you understand by motion under gravity?

Ans: MOTION UNDER GRAVITY:
Motion under gravity is defined as the change in velocity due to the attraction of the Earth. It is called acceleration due to gravity or gravity. It is denoted by “ $g$ ”. The S.I. unit of “ $g$ ” is $m / s^{2}$ or $m s^{- 2}$ .

When a body moves downward, the value of “ $g$ ” is taken as positive (+9.8 m/sec²).
When a body moves upward, the value of “ $g$ ” is taken as negative (-9.8 m/sec²).

When a body falls freely, then equations of motion can be written as:

$v_{f} = v_{i} + g t$ $h = v_{i} t + \frac{1}{2} g t^{2}$ $2 g h = v_{f}^{2} - v_{i}^{2}$

TALEEM

Pages

KINEMATICS OF LINEAR MOTION Chapter # 03 Physics 10th - Question Answers

No comments:

Post a Comment