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Class 9 Describing Motion Around Us Worksheet
Worksheet On Describing Motion Around Us Class 9
Describing Motion Around Us Worksheet Class 9
→ Motion in a Straight Line: When an object moves in a straight line, its motion is called linear motion or motion in a straight line.
→ Describing Position: The method of specifying the location of an object using a reference point.
→ Reference Point: A fixed point or location used to compare and describe the position of other objects.
→ Rest: Position with respect to the reference point does not change.
→ Motion: Position with respect to the reference point changes.
→ Instant of Time: A single reading of a clock at a given point of time.
→ Distance Travelled: The total length of the path covered by an object during motion. It is a scalar quantity and is measured in metres (m).
→ Displacement: The shortest straight-line distance between the initial and final positions of an object, along with direction.
→ Magnitude: Numerical value (with units) of such a physical quantity.
→ Scalar Quantity: A physical quantity that has only magnitude (size) and no direction.
→ Vector Quantity: A physical quantity that has both magnitude and direction.
→ Uniform Motion: Motion in which an object covers equal distances in equal intervals of time, no matter how small the time interval is.
→ Non-uniform Motion: Motion in which an object covers unequal distances in equal intervals of time.
→ Speed: The rate at which an object covers distance. It is calculated as distance divided by time and is a scalar quantity. Speed = Distance / Time
→ Average Speed: The total distance travelled divided by the total time taken during the motion of an object.
→ Velocity: The rate of change of displacement with time. It includes both magnitude and direction, making it a vector quantity.
→ Average Velocity: The total displacement divided by total time taken. It depends on the net change in position, not the total path length.
→ Acceleration: The rate of change of velocity with time. It can occur due to a change in speed, direction, or both. Acceleration = (Final velocity – Initial velocity) / Time
→ Average Acceleration: Total change in velocity divided by the total time taken.
→ Uniform Acceleration: When the velocity of an object changes by equal amounts in equal intervals of time.
→ Non-uniform Acceleration: When the velocity changes by unequal amounts in equal intervals of time.
→ Retardation (Deceleration): Negative acceleration, it occurs when an object slows down.
→ Graphical Representation of Motion: The use of graphs to visually show how quantities like position, velocity, and acceleration change with time.
→ Position-Time Graph (Distance-Time Graph): A graph that shows how the position (or distance) of an object changes with time.
· A straight line indicates uniform motion.
· A curved line indicates non-uniform motion.
→ Velocity-Time Graph: A graph that shows how velocity changes with time.
· A straight horizontal line indicates constant velocity.
· A sloping line or non- straight line indicates acceleration.
→ Slope (Gradient): The steepness of the line in a graph.
· In a position-time graph, slope represents velocity.
· In a velocity-time graph, slope represents acceleration.
→ Area under the Graph: The space between the graph line and the time axis.
· In a velocity-time graph, it represents displacement.
· In a speed-time graph, it represents distance.
→ Kinematic Equations: A set of equations used to describe motion in a straight line with constant acceleration:
· v = u + at
· s = ut + \(\frac{1}{2}\)at2
· v2 = u2 + 2as
where:
u = initial velocity,
v = final velocity,
a = acceleration,
t = time,
s = displacement
→ Motion in a Plane: Motion that occurs in two dimensions (along both x-axis and y-axis).
→ Uniform Circular Motion: Motion of an object along a circular path at constant speed. Even though speed is constant, velocity changes due to a continuous change in its direction.
Class 9 Science Exploration Chapter 4 Worksheet
Class 9 Science Describing Motion Around Us Worksheet
A. Multiple-Choice Questions
Question 1.
A car travels 5 km north, then 12 km east, and finally 5 km south. What is the magnitude of its displacement from the starting point?
(a) 22 km
(b) 12 km
(c) 10 km
(d) 5 km
Question 2.
A runner completes one full lap of a circular track of radius 50 m. Select the correct option,
(a) Distance = 100 m, Displacement = 0
(b) Distance = 314 m, Displacement = 0
(c) Distance = 314 m, Displacement = 100 m
(d) Distance = 100 m, Displacement = 100 m
Question 3.
A car travels 60 km in 2 hours, then 40 km in one hour, all along a straight roa(d) What is its average speed?
(a) 30 km/h
(b) 33.3 km/h
(c) 40 km/h
(d) 50 km/h
Question 4.
A car travels 200 km north in 3 hours, then 200 km south in 2 hours. What are its average speed and average velocity for the entire trip?
(a) Average speed = 80 km/h, Average velocity = 0 km/h
(b) Average speed = 80 km/h, Average velocity = 20 km/h north
(c) Average speed = 40 km/h, Average velocity = 0 km/h
(d) Average speed = 40 km/h, Average velocity = 20 km/h south
Question 5.
Which condition ensures that the magnitude of average velocity is equal to the average speed?
(a) Motion along a straight line without reversal.
(b) Motion along a circular path.
(c) Motion in which the direction changes during motion.
(d) Motion along a curved path is zero.
Question 6.
A bus increases its velocity from 10 m/s to 25 m/s in 5 seconds. What is its average acceleration?
(a) 3 m/s2
(b) 5 m/s2
(c) 7.5 m/s2
(d) 15 m/s2
Question 7.
Which statement is correct about acceleration?
(a) An object moving fast must have high acceleration.
(b) An object moving at constant velocity has zero acceleration.
(c) Acceleration depends only on speed, not direction.
(d) Acceleration is always opposite to velocity.
Question 8.
This question consists of an Assertion (A) and a Reason (R). Read the Assertion and Reason and choose the appropriate answer.
Assertion (A): An object moving at high speed can have zero acceleration.
Reason (R): Acceleration depends on the rate of change of velocity, not on the magnitude of velocity.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.
Question 9.
This question consists of an Assertion (A) and a Reason (R). Read the Assertion and Reason and choose the appropriate answer.
Assertion (A): The magnitude of displacement can never be greater than the total distance travelle(d) Reason (R): Displacement is the shortest path between two points, while distance is the actual path length.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.
Question 10.
This question consists of an Assertion (A) and a Reason (R). Read the Assertion and Reason and choose the appropriate answer.
Assertion (A): In uniform circular motion, the speed of the object remains constant. Reason (R): The velocity of the object also remains constant,
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.
B. State True (T) or False (F).
Question 1.
Displacement of an object can never be zero, if the object has moved.
Question 2.
The speedometer reading is nearly equal to the magnitude of the velocity at an instant.
Question 3.
Average speed depends only on displacement, while average velocity depends only on total distance travelled.
Question 4.
An object moving at constant velocity has zero acceleration.
Question 5.
In uniform circular motion, the speed of the object is constant, but its velocity keeps changing.
C. Fill in the blanks.
Complete the following with a suitable word/ words:
Question 1.
If the net force acting on an object is zero, the object will either remain at rest or move with _______ .
Question 2.
Average velocity = Displacement/ _______.
Question 3.
If a car goes from 10 m s-1 to 0 m s-1 in 5 s, its acceleration is _______.
Question 4.
The slope of a position-time graph gives _______.
Question 5.
The distance covered by an object in one revolution of radius ‘R’ is _______.
D. Assign one word to the following.
Question 1.
The fixed point used to describe the position of an object.
Question 2.
The quantity that tells us how fast an object moves without giving direction.
Question 3.
Motion in which the direction of velocity changes continuously while speed stays constant.
Question 4.
The physical quantity whose SI unit is m s-2.
Question 5.
The type of motion represented by a straight-line position-time graph.
E. Match the Column I with Column II.
Question 1.
| Column I | Column II |
| (i) Uniform motion | (a) Meter per second square |
| (ii) Slope of velocity-time graph | (b) Displacement |
| (iii) Area under velocity-time graph | (c) Constant speed, Changing direction |
| (iv) SI unit of acceleration | (d) Acceleration |
| (v) Uniform circular motion | (e) Straight line (distance-time graph) |
F. Very Short Answer Type Questions
Question 1.
Distinguish between uniform and non-uniform motion with one example of each.
Question 2.
During a road trip, Ramesh drives 150 km east in 2 hours, then 90 km west in 1.5 hours. Calculate his average speed and average velocity.
Question 3.
Write the three kinematic equations for motion in a straight line with constant acceleration.
G. Short Answer Type Questions
Question 1.
A train starts from rest and accelerates uniformly. After 30 seconds it reaches a speed of 54 km/h. Calculate, (a) the acceleration, (b) the distance covered in this time.
Question 2.
During a road trip, a man drives 200 km north in 3 hours and then 200 km south in 2 hours. Calculate the average speed and average velocity for the entire trip.
Question 3.
An object is dropped from rest. Using the experimental data (v = 9.8 m s-1 at t = 1 s; v = 19.6 m s-1 at t- 2 s; v = 29.4 m s-1 at t = 3 s, etc.), show that the acceleration due to gravity is constant and determine its value.
H. Long Answer Type Questions
Question 1.
A train starts from rest and accelerates uniformly. After 30 seconds, it reaches a speed of 54 km/h.
Calculate: (i) the acceleration, (ii) the distance covered in this time.
Question 2.
Derive the kinematic equation v2 = u2 + 2as from the velocity-time graph for an object moving with constant acceleration.
Question 3.
The velocity-time graph from 0 s to 120 s for a cyclist is shown below. Shade the areas (in different colours) representing the displacement of the cyclist (i) while cyclist is moving with constant velocity, (ii) when the velocity of cyclist is decreasing. Also, calculate the displacement and average acceleration in the 120 s time interval.
Wonder Why
A. Give reasons for the following.
Question 1.
A car can be moving at high speed yet have zero acceleration.
Question 2.
The displacement of Sarang is zero after swimming to the other end and back, even though he has covered 50 m.
Question 3.
It is important to maintain a safe distance from the vehicle ahead while driving on the road.
Question 4.
Fuel consumption of a vehicle depends on total distance travelled, not displacement.
Question 5.
A girl is sitting on a merry-go-round. She moves with constant speed along the circular path. Yet, she is said to be accelerating.
Learn By Doing
A. Label the following diagrams.
Question 1.
A skydiver jumps out of a hot-air balloon, which is 4000 m above the ground. At time = 30s, she opens her parachute. The graph is the speed-time graph of her fall.
a. Label with the letter X, the point on the graph where the sky-diver opens her parachute.
b. Label with the letters Y and Z, the two points of the graph where the sky diver falls at a minimum velocity.
Question 2.
Study the velocity-time graph and shade (in different colours) the region showing: (a) displacement during constant velocity phase, and (b) displacement during deceleration phase. Also calculate the total . displacement and the average acceleration in the given time interval.
B. Observe and record.
The table below shows position-time data for two vehicles A and B. Study the data and answer the questions below.
1. Calculate the velocity of vehicle A at any interval of time. Is it uniform?
2. Does vehicle B show uniform or non-uniform motion? How do you conclude?
C. Observe and calculate.
Question 1.
Refer to the position-time graph provided below, which illustrates the motion of an object over a 16 seconds interval. The motion is divided into four distinct regions: A, B, C, and D.
Identify the type of motion in the region A, B, C and D and justify your answer.
Explore With Curiosity
A. A girl walks along a straight path to drop a letter in the letterbox and comes back to her initial position. Her displacement-time graph is shown. Plot a velocity-time graph for the same.
B. Analyse and answer.
Question 1.
A motorbike has an initial velocity of 28 m s-1 and stops after travelling 98 m with constant deceleration. Find: (a) the acceleration, and (b) the time taken to stop.
Question 2.
A bus travelling at 36 km h-1 sees an obstacle 30 m ahead. The driver takes 0.5 s to react before braking. The brakes cause a deceleration of 2.5 m s-2. Will the bus stop on time?
Question 3.
A merry-go-round of radius 3 m completes one revolution in 6 s. Calculate: (a) the distance covered in one revolution, and (b) the displacement after one revolution.
C. Read the following passage and answer the questions below.
Meera is driving on a highway at 108 km h-1. She notices a broken-down vehicle 200 m ahead. Her reaction time is 0.8 s before she presses the brakes. Once the brakes are applied, the car decelerates at 6 m s-2. A vehicle- to-vehicle (V2V) communication system in her car had already alerted her 3 seconds earlier, giving her extra time to slow down to 72 km h-1 before she noticed the obstacle visually.
Question 1.
Without the V2V alert, how far does Meera travel during her reaction time?
Question 2.
Without the V2V alert, calculate the total stopping distance (reaction distance + braking distance). Would she stop on time?
Question 3.
With the V2V alert, she slows to 72 km h-1 first. Recalculate the total stopping distance. How does the V2V system help?
Question 4.
What is the role of velocity in determining stopping distance? Use your calculations to justify.
Suggested Activities
A. Install the Phyphox app on a smartphone. Open ‘Accelerometer (without g)’. Record readings when (a) the phone is on a flat palm, and (b) when you walk holding the phone. Compare the graphs. What do the readings tell you about motion and acceleration in real life? Write your observations below.
B. Create a cardboard disc (radius = 8 cm). Write numbers 1-12 at a distance of 7 cm from the centre and letters A-F at 4 cm from the centre. Spin it at different speeds. Observe that, at certain speeds, the numbers appear blurred but letters remain visible. Calculate and compare the speeds of the numbers and letters. Explain your findings using the concept of uniform circular motion.
C. Talk to a vehicle driver or motor mechanic about factors that affect stopping distance such as wet roads, worn tyres, reaction time, vehicle load, weather conditions. Using your knowledge of kinematic equations, design a safety poster for your school explaining how speed affects stopping distance. Describe the design and key messages of your poster.
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