Test: Motion- 2 - Class 9 MCQ

The equations of motion are applicable only when the body moves with uniform acceleration. A body under constant acceleration is uniformly accelerated motion.

Topic in NCERT: Equations of Motion

Line in NCERT: "The motion of an object moving at uniform acceleration can be described with the help of the following equations, namely v = u + at."

• Displacement is the shortest straight line distance between the initial and final position. This means that there doesn't exist any other path which is shorter than it.
• If the object travels with that shortest straight-line path then the magnitude of distance and displacement would be the same.
• If the object doesn't do so and travels with any other paths then as the other path is not the shortest path, so it will be larger than that of displacement. So if the object travels with this path then the magnitude of displacement will be smaller than the distance.

Thus, the magnitude of displacement may be equal to or smaller than that of distance.

Topic in NCERT: DISPLACEMENT AND DISTANCE

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

v = u + at
or = 2m/s²
s = ut + 
= 100 m

It is horizontal so, angle is zero and also acceleration is zero. Hence constant velocity.

Topic in NCERT: VELOCITY-TIME GRAPHS

Line in NCERT: "If the object moves at uniform velocity, the height of its velocity-time graph will not change with time."

In figure A, we can see that the object continues to remain at a fixed place while the time keeps running. So, the object is at rest, because the object does not change its position with time.

- Assertion (A) is false: The speedometer measures instantaneous speed, not average time or average speed.
- Reason (R) is true: Average velocity is indeed total displacement divided by total time.
- Thus, the correct answer is D: A is false but R is true.
- A speedometer shows how fast a vehicle is moving at a specific moment, not over an entire trip.

- Assertion is false: Acceleration can be negative, positive, or zero, depending on whether the velocity of the body is decreasing, increasing, or constant, respectively.

- Reason is true: Acceleration is indeed the rate of change of velocity.

- Correct option: D. The assertion is false, but the reason is true. Acceleration is not limited to being positive; it reflects any change in velocity's magnitude or direction.

- The assertion is true. Displacement can be zero if an object returns to its starting point, despite having traveled some distance.

- The reason is false. Displacement is the shortest distance between the initial and final positions, not the longer distance.

- Therefore, the correct answer is C: A is true but R is false.

Assertion (A): Incorrect. On a velocity-time graph, uniform acceleration is represented by a straight line, not a parabolic trajectory. A parabolic trajectory is seen on a position-time graph for uniformly accelerated motion.
Reason (R): Incorrect. The distance-time graph for uniform acceleration is not a straight line but a curve. A straight-line distance-time graph indicates uniform velocity, not acceleration.
Explanation: Both the Assertion and Reason are false. The Assertion is incorrect because uniform acceleration on a velocity-time graph is a straight line. The Reason is incorrect as well because uniform acceleration produces a curved distance-time graph.

In uniform circular motion, the object's speed remains constant, but its direction continuously changes. This change in direction means that the velocity is always changing, even though its magnitude remains constant. Thus, the acceleration is always directed towards the center of the circle, causing a change in velocity due to the change in direction.

Topic in NCERT: Uniform Circular Motion

Line in NCERT: "When an object moves in a circular path with uniform speed, its motion is called uniform circular motion."