CBSE Class 9 Science Chapter 04 Describing Motion Around Us MCQs Set 01

Answer: (C) 15 days

Explanation:
Together they cover 9 + 5 = 14 yojanas each day, so covering the full 210 yojanas takes 210/14 = 15 days.

Answer: (B) It keeps moving in the direction it had at the moment of release

Explanation:
Once nothing is guiding the marble along the curve, it simply continues in whatever direction it happened to be moving at that instant, giving a straight path.

Answer: (B) The object's final position coincides with its starting position

Explanation:
Speed depends only on distance covered, but velocity depends on displacement. If the object returns to where it started, displacement is zero, making average velocity zero, while distance covered (and hence average speed) can still be large.

Answer: (C) moving with increasing velocity

Explanation:
Since slope of a position-time graph gives velocity, a curve getting steeper means the velocity itself is growing over time — the hallmark of accelerated motion.

Answer: (B) Distance travelled or displacement

Explanation:
• The graph's slope gives acceleration.
• The enclosed area, however, corresponds to velocity multiplied by time, which is displacement.
• This holds true whether velocity is constant or changing uniformly.

Answer: (B) Because the child ends up at the same point where they started

Explanation:
Displacement only cares about the net change in position between start and end points; after one complete loop the child is back at the starting position, so the net change is zero even though a distance equal to the circumference was covered.

Answer: (B) The car is accelerating because the direction of its velocity keeps changing

Explanation:
Acceleration arises from any change in velocity, and velocity includes direction. Even with an unchanging speedometer reading, the continuously turning direction of motion in a circular path means the car is accelerating.

Answer: (C) Uniform motion covers equal distances in every equal time interval

Explanation:
An object in uniform straight-line motion moves the same distance in every equal chunk of time, keeping its speed constant; unequal distances in equal times instead signal non-uniform motion.

Answer: (C) Its displacement is zero while the total distance travelled is not zero

Explanation:
The ball ends up back where it started, so the net position change (displacement) is zero, even though it actually travelled up and back down, covering a nonzero total distance.

Answer: (B) The acceleration acts opposite to the direction of the bus's velocity

Explanation:
When speed is dropping, the acceleration must point against the direction of motion; the minus sign is simply how this opposing direction is expressed mathematically, not an error or reversal of travel.

Answer: (B) Vehicle B has a greater acceleration than A

Explanation:
Slope on a velocity-time graph represents acceleration, so a steeper line for B means its velocity is increasing faster than A's, i.e., B has greater acceleration.

Answer: (B) Because it serves as a simplified foundation for understanding complex motions like planetary orbits

Explanation:
Like other idealised models discussed in the chapter, uniform circular motion strips away real-world complications so that the basic principles can be applied and later extended to more complicated situations such as planets orbiting the Sun.

Answer: (B) They are always equal

Explanation:
The chapter's note clarifies that when motion happens without any reversal in direction, the total path length covered and the straight-line change in position work out to be numerically the same.

Answer: (B) Find the slope of the line joining the points at 20 s and 40 s

Explanation:
Acceleration is the rate of change of velocity with time, and on a velocity-time graph this rate corresponds precisely to the slope between the two chosen points.

Answer: (C) Acceleration due to gravitational force

Explanation:
This steady gain of 9.8 m/s each second, shown to be the same in every one-second interval of the fall, is identified in the chapter as the acceleration due to gravity, denoted g.

Answer: (A) Its distance and direction from the reference point

Explanation:
Position is described by stating how far the object is from the fixed reference point along with the direction in which it lies from that point. Just the distance alone would leave the location ambiguous, which is why direction is equally essential.

Answer: (B) The numerical value of the quantity along with its units

Explanation:
Magnitude simply refers to the size or numerical value (with appropriate units) of a physical quantity, separate from its direction. For displacement, this numerical value corresponds to the straight-line distance between the two positions.

Answer: (C) Because speed is calculated using distance travelled, which itself has no direction

Explanation:
Average speed comes from dividing total distance travelled by time, and distance is purely a numerical quantity without direction. Since velocity instead uses displacement, which does have a direction, only velocity ends up carrying directional meaning.

Answer: (B) The displacement is zero while the total distance travelled is twice the height reached

Explanation:
Since the ball ends up exactly where it started, there is no net change in position, so displacement works out to zero. However, it still physically covers the upward path and then the same path downward, so the distance travelled is twice the height OB.

Answer: (A) Acceleration depends on how quickly velocity changes, not on how large the speed itself is

Explanation:
Acceleration is tied to the rate of change of velocity over time. If the velocity stays exactly the same from one moment to the next, there is nothing changing, so the acceleration is zero even though the bus itself may be moving very fast.

Answer: (B) metre per second squared (m s-2)

Explanation:
Acceleration measures how velocity changes over time, so its unit combines a velocity unit (m s-1) with a further division by time, giving m s-2.

Answer: (C) The vehicle is stationary at a fixed position away from the origin

Explanation:
Since the position value never changes with time, the object simply is not moving — it is sitting still, just not at the origin but at the 40 m mark. A horizontal line on a position-time graph always signals rest, not motion.

Answer: (D) Average speed

Explanation:
The chapter's 'Ready to Go Beyond' box explains that scalars need only a magnitude, while vectors need both magnitude and direction. Displacement, velocity and acceleration all require a specified direction, but average speed does not — it is derived purely from distance, making it a scalar.

Answer: (B) Aryabhatiya

Explanation:
• The Aryabhatiya, dated to the 5th century CE, is cited as the early source establishing the speed-distance-time relationship.
• The Ganitakaumudi, a 14th century text, is mentioned separately as the source of the postmen problem used to illustrate this idea.

Answer: (B) 4 m s-1

Explanation:
Starting velocity u is 0 since she begins from rest, and acceleration a is 1 m s-2 applied for t = 4 s. Plugging into v = u + at gives v = 0 + (1 x 4) = 4 m s-1.