Ch#2 : Kinematics

Question 1

What is Kinematics? Explain rest and motion.

Answer 1

Kinematics : is the study of the motion of an object without discussing the cause of motion.

A body is said to be in rest , if it doesnt change position with respect to its surroundings.

A body is said to be in motion , if it does change position with respect to its surroundings.

Example : Passenger in a bus are at rest with respect to objects and other passengers in the bus but to a observer outside the bus , the bus and its passengers are in motion.

Question 2

Explain all types of motion with examples

Answer 2

Translatory Motion : is the motion of a body along a line without any rotation.The line can be curved or straight.

Example : Motion of riders of a Ferris Wheel.

Types of translational motion:
1. Linear Motion : Straight line motion of a body is called Linear motion

2. Circular Motion : The motion of an object in a circular path.
3. Random Motion : The random or irregular motion of a body is called random motion.

Rotatory Motion : The spinning motion of a body about its axis.

Vibratory Motion : The to and fro motion of a body about its mean position.

Question 3

What are Scalar and Vector quantities?

Answer 3

Scalar : Scalar Quantities are described by magnitude only.
Example : 5kg , 4s , 1.4m

Vector : Vector Quantities are described by magnitude and direction
Example : 4m , 5m/s

Question 4

What is position? , Differ between distance and displacement.

Answer 4

Position is the location of a point with respect to some reference point called origin.

Distance : Displacement

1. The length of a path between 2 points : The shortest distance between 2 points which has magnitude and direction
2. Scalar : Vector
3. Can be a curved or straight line : Always a straight line
4. Diagram

Question 5

State and explain speed and uniform speed

Answer 5

Definition : Speed is the distance covered in unit time

Speed = Distance/time

Distance = Speed X time

Scalar Quantity , SI Unit : m/s¹

Uniform Speed : If a body covered equal distance in equal intervals of time however short those intervals may be, then it has uniform speed.

Question 6

State and explain velocity and uniform velocity.

Answer 6

Definition : Rate of displacement of a body is called velocity

Velocity = Displacement/time

Displacement = V t

Vector Quantity , SI unit : m/s¹

Uniform Velocity : If a body covers equal displacement in equal intevals of time however short they may be , it has uniform velocity.

Question 7

State and explain acceleration , also describe retardation.

Answer 7

Definition : The rate of change of velocity.

a = Vf - Vi/t

Vector Quantity , SI Unit : m/s²

Uniform Acceleration : If a body has equal changes in velocity in equal intevals of time however short they maybe , it has uniform acceleration.

Acceleration is positive if the velocity increases with time and negative if velocity decreases with time.The direction of negative acceleration is opposite to the direction of the decreasing velocity.
Negative acceleration is called retardation.

Question 8

Distance time graph :

1. When can distance and displacement be used interchangeably?
2. What represents rest , uniform speed and variable speed?

Answer 8

1.If the motion is in a straight line.
2. Rest : Straight line parallel to time-axis.
Uniform speed : Straight line not parallel to time-axis
Variable speed : Curved line

Question 9

Derive the 3 equations of motion.

Answer 9

Note : SIMPLIFIED
First equation of motion:
a = Vf - Vi/t
at = Vf - Vi
Vf = at + Vi

Second Equation of motion:
Distance S is the area under the graph ,
S = area of rect + area of triangle
S = Vi x t + 1/2at²

Third Equation of motion :
The area under the graph is S
S = sum of parallel sides/2 X height
2S = (Vf + Vi) X t
Multiply b/s by a
2aS = (Vf + Vi)(Vf - Vi)
2aS = Vf² - Vi²

Question 10

Write the equations of motion for bodies moving under gravity.

Answer 10

Vf = Vi + gt
h = Vi x t + 1/2at²
2gh = Vf² - Vi²