Extra 30 short questions and answers from the Motion chapter:8 of Class 9 CBSE Science:
Define uniform and non-uniform motion with examples.
Answer:
Uniform Motion: When a body covers equal distances in equal intervals of time, it is in uniform motion. (Example: A car moving at 60 km/h on a straight road).
Non-uniform Motion: When a body covers unequal distances in equal intervals of time, it is in non-uniform motion. (Example: A bus slowing down to stop at a traffic signal.)
Differentiate between distance and displacement.
Answer:
Distance: The total path covered by an object (scalar quantity).
Displacement: The shortest straight-line path between the initial and final positions (vector quantity).
State and explain the three equations of motion.
Answer:
First Equation: v=u+atv = u + atv=u+at (velocity-time relation).
Second Equation: s=ut+12at2s = ut + \frac{1}{2} at^2s=ut+21at2 (displacement-time relation).
Third Equation: v2=u2+2asv^2 = u^2 + 2asv2=u2+2as (velocity-displacement relation).
What is acceleration? Give its SI unit and types.
Answer:
Acceleration is the rate of change of velocity. SI unit: m/s².
Types:
Positive acceleration (velocity increases).
Negative acceleration or retardation (velocity decreases).
Define average speed and average velocity.
Answer:
Average Speed: Total distance travelled / Total time taken.
Average Velocity: Total displacement / Total time taken.
What is meant by instantaneous velocity?
Answer:
Instantaneous velocity is the velocity of an object at a specific instant of time.
A car moves with a speed of 20 m/s for 10 seconds and then with 30 m/s for the next 10 seconds. Find its average speed.
Answer:
Distance in first 10 s = 20×10=20020 \times 10 = 20020×10=200 m
Distance in next 10 s = 30×10=30030 \times 10 = 30030×10=300 m
Total distance = 200+300=500200 + 300 = 500200+300=500 m
Total time = 20 s
Average speed = 50020=25\frac{500}{20} = 2520500=25 m/s
Explain the velocity-time graph for uniform acceleration.
Answer:
A velocity-time graph for uniform acceleration is a straight line sloping upwards, indicating a constant increase in velocity with time.
What does the slope of a velocity-time graph represent?
Answer:
The slope of a velocity-time graph represents acceleration.
A car accelerates from rest at 5 m/s² for 6 seconds. Find its final velocity.
Answer:
Given: u=0u = 0u=0, a=5a = 5a=5 m/s², t=6t = 6t=6 s
Using v=u+atv = u + atv=u+at,
v=0+(5×6)=30v = 0 + (5 \times 6) = 30v=0+(5×6)=30 m/s
Define retardation and give an example.
Answer:
Retardation (negative acceleration) is a decrease in velocity over time. Example: A car coming to a stop.
What is the area under a velocity-time graph?
Answer:
It represents the
distance travelled
by an object.
Draw and explain the distance-time graph for uniform motion.
Answer:
The distance-time graph for uniform motion is a straight line with a constant positive slope.
Differentiate between speed and velocity.
Answer:
Speed: Scalar quantity, no direction, always positive.
Velocity: Vector quantity, direction matters, can be negative.
How can an object have constant speed but changing velocity?
Answer:
In
circular motion
, speed remains constant but direction changes, so velocity changes.
State an example where distance and displacement are different.
Answer:
A person walking around a circular park and returning to the same point has a distance covered but zero displacement.
Define uniform circular motion.
Answer:
Motion in a circular path at a constant speed (e.g., Earth’s revolution around the Sun).
Why is circular motion an example of acceleration?
Answer:
Because direction changes continuously, so velocity changes, leading to acceleration.
What is the nature of the displacement-time graph for uniform motion?
Answer:
A straight line with a constant slope.
What is meant by non-uniform acceleration?
Answer:
When acceleration is not constant over time.
If a car stops in 5 seconds after applying brakes with an initial velocity of 20 m/s, find acceleration.
Answer: Using v=u+atv = u + atv=u+at,
0=20+5a0 = 20 + 5a0=20+5a,
a=−4a = -4a=−4 m/s² (retardation).
How does the speedometer of a car work?
Answer:
It measures
instantaneous speed
of the vehicle.
Differentiate between instantaneous speed and average speed.
Answer:
Instantaneous speed is at a particular
moment,
average speed is over a time period.
Why is displacement sometimes zero but distance is not?
Answer:
If an object returns to its starting point, displacement is zero, but distance is the total path
traveled
.
Define free fall and give an example.
Answer:
Motion under gravity alone, without any resistance. Example: A dropped ball.
A bike increases its speed from 10 m/s to 30 m/s in 4 seconds. Find acceleration.
Answer:
Using a=v−uta = \frac{v - u}{t}a=tv−u,
a=30−104=5a = \frac{30 - 10}{4} = 5a=430−10=5 m/s²
What is relative motion?
Answer:
Motion observed with respect to another moving object.
State the differences between uniform motion and uniformly accelerated motion.
Answer:
Uniform motion: Constant velocity, no acceleration.
Uniformly accelerated motion: Velocity changes at a constant rate.
