Physics - Class X - Chapter No.3 - Questions And Answers

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KINEMATICS OF LINEAR MOTION

IMPORTANT QUESTIONS FROM PAST PAPERS

1.Define scalar and vector quantities with examples. ( 2012)
2.With the help of vf, vi, a and t derive the equation of motion. (2013)
3.Derive the second equation of motion. (2014)
4.Prove that vf = vi + at. ( 2014)
5.Derive equation 2as = vf2 - v 2.(2010) and ( 2015)

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IMPORTANT SYMBOLS:

•S = distance covered
•V = speed
•t = time
•V_i = initial velocity
•V_f = final velocity
•∆V = change in velocity
•a = acceleration
•g = gravity

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IMPORTANT FORMULA’S:

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Questions / Answers

Q.1)Define the following terms with formula’s and units also.
i.Mechanics , ii. Kinematics, iii. Dynamics, iv. Rest v. Motion, vi. Distance, vii. Displacement, viii. Speed, ix. Velocity, x. Acceleration
Ans:
i.Mechanics: The branch of physics which deals with the objects which are in state of rest or in a state of motion is called mechanics.

ii.Kinematics: The branch of physics which deals with the description of motion of object without reference t the force or agent causing motion is called Kinematics.

iii.Dynamics: Dynamics deals with the forces and their action on the motion of the body is called dynamics.

iv.Rest: A body is said to be in the state of rest if it does not change its position with respect to its surrounding. For example a book lying on the table.

v.Motion: A body is said to be in the state of motion if it changes its position with respect to its surrounding. For example a car moving on the road.

vi.Distance:  The total length covered by a body between two points in any direction is called distance. It is denoted by s.
Nature: It is scalar quantity.
Unit: The unit of distance is meter (m).

vii.Displacement: It is the minimum distance covered in particular direction. It is denoted by d.
Nature: It is vector quantity.
Unit: The unit of displacement is meter (m).

viii.Speed: Distance covered by the body in unit time is called speed. It is denoted by V.
Nature: It is scalar quantity.
Formula: 

Unit: The unit of speed is meter per second (ms^-1 or m/s).

ix.Velocity: Distance covered by the body in unit time in a particular direction is called velocity. It is denoted by V.
Nature: It is vector quantity.
Formula:

Unit: The unit of velocity is meter per second (ms^-1 or m/s).

x.Acceleration: The rate of change of velocity in unit time is called acceleration. It is denoted by a.
Nature: It is vector quantity.
Formula:

Unit: The unit of acceleration is m/s².

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Q.2)Write down the types of motion.
Ans: There are three types of motion.
i. Translatory “or” linear motion: When the body moves on a straight path and the direction of the motion remain constant during motion, its motion is called translatory or linear motion.
For example motion of car and boat.

ii.Rotatory “or” Rational “or” Circular motion: When an object spins or rotates about fixed point or axis, its motion is called Rotatory or Rational or Circular motion.
For example motion of fan and planet around the sun.

iii.Oscillatory “or” vibratory motion: When a body moves to and fro about its mean position, its motion is called oscillatory or vibratory motion.
For example motion of pendulum of a clock.

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Q.3)Define scalar and vector quantity with examples.
Ans:
i.Scalar quantity: Physical quantities, which are completely specified by their magnitude only, are called scalar quantities. it is denoted by —
Example: Time, Mass, Distance, Work, Energy, Temperature,  etc.

ii.Vector quantity: Physical quantities, which are completely specified by their magnitude and direction both, are called vector quantities. It is denoted by →
Example: Displacement, Velocity, Acceleration, Force, Weight, Torque, Momentum etc.

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Q.4)Derive the First, Second and third equation of motion.
Ans: First equation of Motion: (v_f = v_i + at)
Consider a body is moving with initial velocity “v_i” with uniform acceleration “a”. After certain interval of time “t”, its final velocity becomes “v_f”.
Mathematically:

Change in velocity = V_f - V_i  

Change in velocity in unit time = V_f - V_i / t

a = V_f - V_i  / t

at = V_f - V_i

V_f = V_i+ at

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Second Equation of Motion: ( S = V_i t + ¹/₂ at² ):
“Consider a body is moving with initial velocity “V_i” with uniform acceleration “a”. After
certain interval of time “t”, its final velocity becomes “V_f”.
Mathematically:

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Third Equation of Motion:(2aS = V_f² – V_i²)
Consider a body is moving with initial velocity “V_i” with uniform acceleration “a”. After certain interval of time “t”, its final velocity becomes “V_f”. During such duration ii covered distance “s” with uniform acceleration “a”.
Mathematically:

Q. 5)What do you under stand by motion under gravity?
Ans: Motion under Gravity: (Free Fall Motion):
“When a body falls in such a way that no other force accepts the weight acting on it, then such motion is called free fall motion. Its velocity increases continuously till it strikes the ground and then a body get some acceleration which is called acceleration due to gravity and it is define as follow:

“The acceleration produces in a free falling body due to force of gravity is called acceleration due to gravity.”

• When a body moves downward the value of “g” taken positive (9.8 m/sec²) .
•When a body moves upward the value of “g” taken negative (-9.8 m/sec²) .
• Acceleration due to gravity is denoted by “g”.