Rest and Motion / विराम एवं गति
An object is said to be in motion when its position changes with time relative to a chosen reference point.
जब किसी संदर्भ बिंदु के सापेक्ष समय के साथ किसी वस्तु की स्थिति बदलती है, तो वह गति में कहलाती है।
Motion and rest are relative.
गति और विराम सापेक्ष होते हैं।
A passenger sitting in a moving train is at rest relative to the train but moving relative to the ground.
Distance / दूरी
Distance is the total path length travelled.
दूरी वस्तु द्वारा तय किए गए कुल पथ की लंबाई है।
It is a scalar quantity.
यह अदिश राशि है।
SI unit:
metre (m)
Displacement / विस्थापन
Displacement is the shortest straight-line change from initial to final position, with direction.
विस्थापन प्रारंभिक और अंतिम स्थिति के बीच दिशा सहित सबसे छोटा सीधा परिवर्तन है।
It is a vector quantity.
यह सदिश राशि है।
Important Relation
Distance ≥ magnitude of displacement
Distance can never be less than displacement magnitude.
दूरी कभी भी विस्थापन के परिमाण से कम नहीं हो सकती।
Speed / चाल
Speed = Distance / Time
It is scalar.
SI unit:
m/s
Velocity / वेग
Velocity = Displacement / Time
Velocity has direction.
वेग में दिशा शामिल होती है।
It is a vector quantity.
Uniform Motion / समान गति
If an object covers equal distances in equal intervals of time, its motion is uniform.
यदि कोई वस्तु समान समयांतराल में समान दूरी तय करती है, तो गति समान होती है।
Acceleration / त्वरण
Acceleration is the rate of change of velocity.
a = (v−u)/t
where:
u = initial velocity
v = final velocity
t = time
SI unit:
m/s²
Equations of Motion
For uniformly accelerated straight-line motion:
v = u + at
s = ut + ½at²
v² = u² + 2as
These equations are extremely important for SSC and Railway science.
Conversion of Speed
km/h → m/s
Multiply by:
5/18
Example:
72 km/h
=72×5/18
= 20 m/s
m/s → km/h
Multiply by:
18/5
20 m/s
= 72 km/h
Motion Practice — 30 Questions
Q1
SI unit of distance:
Answer: metre
Q2
Distance is:
A. Scalar
B. Vector
Answer: A
Q3
Displacement is:
Answer: Vector / सदिश
Q4
Speed equals:
Answer: Distance ÷ Time
Q5
Velocity equals:
Answer: Displacement ÷ Time
Q6
SI unit of speed:
Answer: m/s
Q7
SI unit of acceleration:
Answer: m/s²
Q8
Rate of change of velocity is:
Answer: Acceleration
Q9
Which can be zero after a round trip?
A. Distance
B. Displacement
Answer: B
Q10
A person completes one full circular lap. His displacement is:
Answer: Zero
Q11
Can distance be non-zero while displacement is zero?
Answer: Yes
Q12
72 km/h equals:
Answer: 20 m/s
Q13
54 km/h equals:
Answer: 15 m/s
Q14
10 m/s equals:
Answer: 36 km/h
Q15
25 m/s equals:
Answer: 90 km/h
Q16
A car covers 150 km in 3 hours. Speed?
Answer: 50 km/h
Q17
A body moves 100 m in 20 s. Speed?
Answer: 5 m/s
Q18
Initial velocity=10 m/s, acceleration=2 m/s², time=5 s. Final velocity?
v=10+2×5
Answer: 20 m/s
Q19
A body starts from rest with acceleration 4 m/s² for 3 s. Final velocity?
Answer: 12 m/s
Q20
u=0, a=2 m/s², t=5 s. Distance?
s=½×2×25
Answer: 25 m
Q21
u=10 m/s, a=2 m/s², t=4 s. Distance?
s=10×4+½×2×16
=40+16
Answer: 56 m
Q22
Which equation is correct?
A. v=u+at
B. v=u−st always
C. s=v/t
D. a=ut
Answer: A
Q23
Which is correct?
Answer: v²=u²+2as
Q24
Motion with constant velocity has acceleration:
Answer: Zero
Q25
Negative acceleration is commonly called:
Answer: Retardation/deceleration
Q26
A speedometer measures:
Answer: Speed
Q27
An odometer measures:
Answer: Distance travelled
Q28
Slope of a distance-time graph represents:
Answer: Speed
Q29
Slope of a velocity-time graph represents:
Answer: Acceleration
Q30
Area under a velocity-time graph gives:
Answer: Displacement