Lakhmir Singh & Manjit Kaur Test: Motion - Class 9 MCQ

Vector Quantity

• Direction: A vector quantity has a specific direction in space. This means that not only does it have a magnitude, but it also has a specific orientation or direction in which it is pointing.
• Magnitude: In addition to having a direction, a vector quantity also has a magnitude. This magnitude represents the size or strength of the vector, indicating how much of the quantity is present.
• Both Magnitude and Direction: Therefore, a vector quantity possesses both magnitude and direction, distinguishing it from scalar quantities which only have magnitude. This dual nature of vectors allows for a more detailed description of physical quantities.

Topic in NCERT: SPEED WITH DIRECTION
Line in NCERT: "The quantity that specifies both these aspects is called velocity."

• Odometer of automobiles records distance travelled.
• The primary function of an odometer in automobiles is to measure and display the total distance the vehicle has traveled since it was first put into use.
• This distance is usually displayed in kilometers or miles depending on the unit system used in the region.

Topic in NCERT: Example 7.2

Line in NCERT: "The odometer of a car reads 2000 km at the start of a trip and 2400 km at the end of the trip."

Speedometer Measurement

• Instantaneous Speed: The speedometer of a car measures the instantaneous speed at any given moment.
• It provides a real-time reading of how fast the car is moving at that particular moment.
• This measurement is important for drivers to ensure they are following speed limits and driving safely.
• It helps drivers make adjustments to their speed based on road conditions, traffic, and other factors.

• A displacement–time graph shows how displacement changes with time.

• If the graph is parallel to the time axis, it means that displacement is not changing over time.

• This implies the particle is not moving, i.e., displacement is constant.

• Velocity = change in displacement / time
  Since displacement doesn't change, the numerator is zero, so:

• Velocity = Displacement/ Time = 0/Time = 0

• Displacement is the straightest shot (shortest distance) between start and end.
• Distance is the total path taken.
• Imagine going for a walk around a block - the displacement is the length of one side, while the distance is the entire walk.
• The numerical ratio of displacement to distance is calculated as displacement divided by distance.
• So the ratio:
• Can be 1 (straight path)
• Is less than 1 (curved path or going back and forth)
• Never more than 1

Therefore, the answer is D: equal to or less than 1.

Topic in NCERT: MOTION ALONG A STRAIGHT LINE

Line in NCERT: "The magnitude of displacement (35 km) is not equal to the path length (85 km)."

• Displacement is the straight line distance between the starting and ending points of an object's motion.
• In this scenario, the body starts at A, goes to B, and then returns to A. Even though the body travels a certain distance (twice the distance between A and B), it ends up back at its starting point (A).
• Since displacement considers the net change in position, and the body ends at the same point it started, the displacement is zero.

Topic in NCERT: Motion Along a Straight Line

Line in NCERT: "the final position coincides with the initial position, and therefore, the displacement is zero."

• In a distance-time graph, the slope or gradient. The greater the gradient, the greater the rate of change.
• The line is equal to the speed of the object.
• The steeper the line (and the greater the gradient) the faster the object is moving.

Topic in NCERT: DISTANCE–TIME GRAPHS

Line in NCERT: "Thus, the graph shown in Fig. 7.4 indicates that a steep slope represents faster motion."

• Option B is correct because Car B has the flattest slope in its distance-time graph, indicating it covers the least distance in a given time and thus is the slowest among the four cars.

Displacement = Area under the velocity-time graph  slope till 5 seconds
The slope is a straight line, and thus its area will be equal to the area of the triangle with height = 20 and base = 5

Area of triangle = 1/2 x base x height

Area = 1/2 x 5 x 20 = 50 m.

When a boy rides a merry-go-round at a constant speed of 10 m/s, he is experiencing:

The boy is in accelerated motion despite moving at a constant speed. This is because:

• His direction is constantly changing as he moves in a circular path.
• Acceleration occurs when there is a change in velocity, which includes changes in direction.
• Thus, even with a constant speed, the boy is not in uniform motion.