🚀 Motion – Class 9 Science MCQs

Section 3: Acceleration & Graphical Representation of Motion (Q51–Q75)

Q51. Acceleration is defined as:

A. Change in velocity per unit time
B. Distance per unit time
C. Displacement per unit time
D. Change in speed per unit distance

✅ Correct Answer: A. Change in velocity per unit time

Explanation:

• A. Correct, a = Δv / Δt.
• B. Distance/time = speed.
• C. Displacement/time = velocity.
• D. Incorrect.

Q52. SI unit of acceleration is:

A. m/s
B. m/s²
C. km/h²
D. cm/s

✅ Correct Answer: B. m/s²

Explanation:

• A. Unit of velocity.
• B. Correct, acceleration = velocity ÷ time = m/s².
• C. Not SI unit.
• D. Wrong unit.

Q53. Negative acceleration is also called:

A. Uniform acceleration
B. Retardation
C. Positive acceleration
D. Uniform velocity

✅ Correct Answer: B. Retardation

Explanation:

• A. Uniform acceleration = positive or negative.
• B. Correct, retardation = decrease in velocity with time.
• C. Opposite.
• D. Wrong.

Q54. A car slows down from 20 m/s to 10 m/s in 5 s. Acceleration = ?

A. 2 m/s²
B. –2 m/s²
C. –5 m/s²
D. 5 m/s²

✅ Correct Answer: B. –2 m/s²

Explanation:

• Formula: a = (v – u)/t = (10 – 20)/5 = –10/5 = –2 m/s².
• Negative → retardation.

Q55. Uniform acceleration means:

A. Acceleration changes with time
B. Acceleration remains constant
C. Speed is constant
D. Velocity is zero

✅ Correct Answer: B. Acceleration remains constant

Explanation:

• A. Wrong.
• B. Correct, equal velocity change in equal times.
• C. That means zero acceleration.
• D. Wrong.

Q56. Acceleration of a body moving with uniform velocity is:

A. Positive
B. Negative
C. Zero
D. Variable

✅ Correct Answer: C. Zero

Explanation:

• A, B. Not applicable.
• C. Correct, velocity doesn’t change → acceleration = 0.
• D. Wrong.

Q57. Which physical quantity is equal to slope of velocity-time graph?

A. Displacement
B. Acceleration
C. Distance
D. Speed

✅ Correct Answer: B. Acceleration

Explanation:

• A. Wrong.
• B. Correct, slope of v–t graph = acceleration.
• C. Wrong.
• D. Not always.

Q58. Which physical quantity is equal to slope of distance-time graph?

A. Acceleration
B. Velocity (or speed)
C. Force
D. Momentum

✅ Correct Answer: B. Velocity (or speed)

Explanation:

• A. Not correct.
• B. Correct, slope of distance-time = speed/velocity.
• C. Wrong.
• D. Wrong.

Q59. Area under velocity-time graph represents:

A. Displacement
B. Acceleration
C. Force
D. Speed

✅ Correct Answer: A. Displacement

Explanation:

• A. Correct, displacement = area under v–t graph.
• B. Slope gives acceleration, not area.
• C, D. Wrong.

Q60. A body starts from rest, u = 0, after 4 s velocity = 20 m/s. Acceleration = ?

A. 5 m/s²
B. 10 m/s²
C. 2 m/s²
D. 4 m/s²

✅ Correct Answer: A. 5 m/s²

Explanation:

• a = (v – u)/t = (20 – 0)/4 = 20/4 = 5 m/s².

Q61. Which type of graph represents uniform acceleration?

A. Straight line in velocity-time graph
B. Curve in distance-time graph
C. Horizontal line in velocity-time graph
D. Parabola in acceleration-time graph

✅ Correct Answer: A. Straight line in velocity-time graph

Explanation:

• A. Correct, constant slope = uniform acceleration.
• B. Shows non-uniform velocity.
• C. Shows zero acceleration.
• D. Wrong.

Q62. If velocity-time graph is a horizontal line parallel to time axis, acceleration is:

A. Positive
B. Negative
C. Zero
D. Cannot say

✅ Correct Answer: C. Zero

Explanation:

• Horizontal v–t graph = constant velocity → zero acceleration.

Q63. In a velocity-time graph, uniform acceleration is shown by:

A. Straight line inclined to time axis
B. Straight line parallel to time axis
C. Curve
D. Vertical line

✅ Correct Answer: A. Straight line inclined to time axis

Explanation:

• A. Correct, slope = constant.
• B. Zero acceleration.
• C. Non-uniform acceleration.
• D. Not valid.

Q64. Which graph can never be obtained in case of uniform acceleration?

A. Straight line velocity-time graph
B. Straight line distance-time graph
C. Curved distance-time graph
D. Curved velocity-time graph

✅ Correct Answer: B. Straight line distance-time graph

Explanation:

• A. Possible (uniform acceleration).
• B. Wrong, for uniform acceleration distance-time graph is parabolic (curved), not straight.
• C. Correct possible.
• D. Possible for non-uniform acceleration.

Q65. Which graph gives information of speed only, not direction?

A. Distance-time
B. Displacement-time
C. Velocity-time
D. Acceleration-time

✅ Correct Answer: A. Distance-time

Explanation:

• A. Correct, distance-time = scalar, no direction.
• B. Displacement-time = direction included.
• C. Velocity-time = vector.
• D. Acceleration-time = vector.

Q66. A car starts from rest and attains 30 m/s in 10 s. Acceleration = ?

A. 2 m/s²
B. 3 m/s²
C. 5 m/s²
D. 10 m/s²

✅ Correct Answer: B. 3 m/s²

Explanation:

• a = (30 – 0)/10 = 30/10 = 3 m/s².

Q67. A uniformly accelerated body covers equal distances in equal time intervals – True or False?

A. True
B. False

✅ Correct Answer: B. False

Explanation:

• Uniform acceleration → equal velocity change in equal times, not equal distance. Distances increase progressively.

Q68. If acceleration is zero, velocity-time graph is:

A. Straight line parallel to x-axis
B. Straight line parallel to y-axis
C. Straight line inclined
D. Parabola

✅ Correct Answer: A. Straight line parallel to x-axis

Explanation:

• A. Correct, constant velocity.
• B. Not valid.
• C. Inclined → acceleration.
• D. Wrong.

Q69. The motion of a freely falling body is an example of:

A. Uniform speed
B. Uniform acceleration
C. Non-uniform acceleration
D. Retardation

✅ Correct Answer: B. Uniform acceleration

Explanation:

• Free fall acceleration due to gravity (g = 9.8 m/s² constant).

Q70. If initial velocity = 0, displacement-time graph under uniform acceleration is:

A. Straight line
B. Parabola
C. Curve opening downward
D. Horizontal line

✅ Correct Answer: B. Parabola

Explanation:

• Equation s = ½ at² → quadratic → parabolic graph.

Q71. Which of these quantities is represented by slope of displacement-time graph?

A. Speed/Velocity
B. Acceleration
C. Force
D. Momentum

✅ Correct Answer: A. Speed/Velocity

Explanation:

• Slope = rate of displacement change = velocity.

Q72. If velocity-time graph is a straight line inclined upwards, motion is:

A. Uniformly accelerated
B. Uniform velocity
C. Retarded
D. Oscillatory

✅ Correct Answer: A. Uniformly accelerated

Explanation:

• Slope positive & constant → uniform acceleration.

Q73. If slope of velocity-time graph is negative, body is:

A. Accelerated
B. Retarded
C. At rest
D. Uniformly moving

✅ Correct Answer: B. Retarded

Explanation:

• Negative slope → velocity decreasing → retardation.

Q74. What does the slope of a speed-time graph give?

A. Displacement
B. Velocity
C. Acceleration
D. Distance

✅ Correct Answer: C. Acceleration

Explanation:

• Slope of speed-time (magnitude only) = acceleration magnitude.

Q75. Which graph can be used to calculate displacement directly by finding area?

A. Distance-time graph
B. Velocity-time graph
C. Acceleration-time graph
D. Speed-time graph

✅ Correct Answer: B. Velocity-time graph

Explanation:

• Area under v–t graph = displacement.
• Other graphs don’t give displacement directly.

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