Motion and Time — Class 7 Science NCERT Solutions (Free)
Free step-by-step NCERT solutions for Class 7 Science chapter "Motion and Time" — 8 important questions with detailed answers for CBSE board exam preparation.
TL;DR: Free step-by-step NCERT solutions for Class 7 Science chapter "Motion and Time" — 8 important questions with detailed answers for CBSE board exam prep…
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NCERT Solutions for Class 7 Science — Motion and Time. Step-by-step answers to all 8 textbook questions from this chapter, written for CBSE board preparation and free to use.
Motion and Time — All 8 Questions Solved
Q1. Define motion. Give examples of motion and rest.
Motion: change in position of an object with respect to a reference point over time. Examples of motion: car moving on road, bird flying, falling ball. Examples of rest: book on table, person sitting on chair, building.
Note: Motion and rest are relative - depend on reference point chosen.
Q2. Calculate speed if distance = 150 km and time = 3 hours.
Step 1: Formula = Speed = Distance / Time
Step 2: Speed = 150 km / 3 h
Step 3: Speed = 50 km/h
Answer: Speed is 50 km per hour.
Q3. A car travels 200 m in 10 seconds. Calculate its speed in m/s and km/h.
Step 1: Speed = Distance / Time = 200 m / 10 s = 20 m/s
Step 2: Convert m/s to km/h: Multiply by 3.6 (or 18/5)
Step 3: 20 m/s × 3.6 = 72 km/h
Answer: Speed = 20 m/s = 72 km/h
Q4. What is the difference between speed and velocity?
Speed: distance traveled per unit time; scalar quantity (only magnitude); always positive.
Velocity: displacement per unit time; vector quantity (magnitude + direction); can be positive or negative.
Example: 60 km/h is speed; 60 km/h north is velocity.
Formula: Speed = Distance/Time; Velocity = Displacement/Time
Q5. What is acceleration? Give examples.
Acceleration: rate of change of velocity with time. It measures how quickly an object speeds up, slows down, or changes direction. Formula: a = (v - u) / t where v = final velocity, u = initial velocity, t = time.
Examples: Car increasing speed (positive acceleration), car braking (negative acceleration/deceleration), circular motion (change in direction).
Q6. A bus accelerates from rest to 30 m/s in 10 seconds. Calculate acceleration.
Step 1: Initial velocity u = 0 m/s (starts from rest)
Step 2: Final velocity v = 30 m/s, Time t = 10 s
Step 3: Acceleration a = (v - u) / t = (30 - 0) / 10
Step 4: a = 30 / 10 = 3 m/s²
Answer: Acceleration = 3 m/s²
Q7. What are different types of motion? Explain with examples.
Types of motion:
1. Linear motion: movement in straight line (train on track, arrow shot)
2. Circular motion: movement along circular path (earth around sun, fan blade)
3. Oscillatory motion: repeated back-and-forth movement (pendulum, swing)
4. Random motion: unpredictable movement (gas molecules, dust particle in air)
Q8. What is a speedometer? How does it measure speed?
Speedometer: instrument in vehicles that displays instantaneous speed (speed at any given moment). Located on dashboard. Measures speed by: mechanical linkage to wheels (older cars) or electronic sensors detecting wheel rotation. Scale shows speed in km/h or m/s. Different vehicles have different maximum speed limits shown on scale.
Motion and Time — Practice MCQs with Answers
Attempt these 20 multiple-choice questions after working through the solutions above. Each carries the correct option and the reasoning behind it, so a wrong answer tells you which idea to revisit.
MCQ 1. What is the SI unit of time?
- A. Hour
- B. Minute
- C. Second
- D. Day
Answer: C. Second — The SI (International System of Units) unit for time is the second. Other units like hour, minute, and day are commonly used but are not the SI unit.
MCQ 2. Which of the following is an example of rectilinear motion?
- A. Motion of a merry-go-round
- B. Motion of a car on a straight road
- C. Motion of a swinging pendulum
- D. Motion of the Earth around the Sun
Answer: B. Motion of a car on a straight road — Rectilinear motion is motion along a straight line. A car moving on a straight road exhibits this type of motion.
MCQ 3. A car travels a distance of 180 km in 3 hours. What is its average speed?
- A. 50 km/h
- B. 60 km/h
- C. 70 km/h
- D. 183 km/h
Answer: B. 60 km/h — Speed is calculated as Distance / Time. So, 180 km / 3 hours = 60 km/h.
MCQ 4. The device used to measure the distance covered by a vehicle is called:
- A. Speedometer
- B. Odometer
- C. Thermometer
- D. Barometer
Answer: B. Odometer — An odometer is an instrument used to measure the total distance traveled by a vehicle. A speedometer measures the instantaneous speed.
MCQ 5. What type of motion does a swinging pendulum exhibit?
- A. Rectilinear motion
- B. Circular motion
- C. Oscillatory motion
- D. Rotational motion
Answer: C. Oscillatory motion — A swinging pendulum moves to and fro about a mean position, which is characteristic of oscillatory motion.
MCQ 6. A simple pendulum takes 20 seconds to complete 10 oscillations. What is its time period?
- A. 2 seconds
- B. 0.5 seconds
- C. 20 seconds
- D. 10 seconds
Answer: A. 2 seconds — The time period is the time taken for one oscillation. So, 20 seconds / 10 oscillations = 2 seconds per oscillation.
MCQ 7. Which of the following units is used to measure speed?
- A. Kilogram
- B. Metre
- C. Metre per second (m/s)
- D. Litre
Answer: C. Metre per second (m/s) — Speed is distance divided by time. Therefore, its unit is a unit of distance divided by a unit of time, such as metres per second (m/s) or kilometres per hour (km/h).
MCQ 8. If a car covers unequal distances in equal intervals of time, its motion is said to be:
- A. Uniform motion
- B. Non-uniform motion
- C. Rectilinear motion
- D. Periodic motion
Answer: B. Non-uniform motion — Non-uniform motion occurs when an object covers unequal distances in equal intervals of time, meaning its speed is changing.
MCQ 9. What is the formula for calculating speed?
- A. Speed = Time / Distance
- B. Speed = Distance × Time
- C. Speed = Distance + Time
- D. Speed = Distance / Time
Answer: D. Speed = Distance / Time — Speed is defined as the distance covered per unit of time. Hence, the formula is Speed = Distance / Time.
MCQ 10. Which of the following statements about a distance-time graph represents an object at rest?
- A. A straight line parallel to the time axis
- B. A straight line parallel to the distance axis
- C. A straight line passing through the origin
- D. A curved line
Answer: A. A straight line parallel to the time axis — When an object is at rest, its distance from the origin does not change with time. This is represented by a horizontal straight line (parallel to the time axis) on a distance-time graph.
MCQ 11. What was an ancient device used to measure time based on shadows?
- A. Water clock
- B. Sand clock
- C. Sundial
- D. Pendulum clock
Answer: C. Sundial — A sundial uses the position of a shadow cast by the sun to indicate the time of day. It was one of the earliest methods of time measurement.
MCQ 12. The SI unit of distance is:
- A. Kilometre
- B. Centimetre
- C. Metre
- D. Millimetre
Answer: C. Metre — The SI (International System of Units) unit for length or distance is the metre. Other units are common but metre is the standard.
MCQ 13. A train moves at a constant speed of 72 km/h. How much distance will it cover in 30 minutes?
- A. 36 km
- B. 24 km
- C. 72 km
- D. 144 km
Answer: A. 36 km — First, convert 30 minutes to hours (0.5 hours). Then, Distance = Speed × Time = 72 km/h × 0.5 h = 36 km.
MCQ 14. The time period of a simple pendulum depends on its:
- A. Mass of the bob
- B. Amplitude of oscillation
- C. Length of the string
- D. Material of the string
Answer: C. Length of the string — The time period of a simple pendulum primarily depends on its length. It is nearly independent of the mass of the bob and the amplitude (for small amplitudes).
MCQ 15. Which of these is an example of circular motion?
- A. A stone falling from a height
- B. Blades of a rotating fan
- C. A shuttlecock in badminton
- D. A child sliding down a slide
Answer: B. Blades of a rotating fan — Circular motion is motion along a circular path. The blades of a rotating fan move in a circle around a central axis.
MCQ 16. If an object travels 100 meters in 10 seconds, what is its speed in m/s?
- A. 1 m/s
- B. 10 m/s
- C. 100 m/s
- D. 0.1 m/s
Answer: B. 10 m/s — Speed = Distance / Time. So, 100 meters / 10 seconds = 10 m/s.
MCQ 17. The motion of the Earth around the Sun is an example of:
- A. Rectilinear motion
- B. Rotational motion
- C. Circular motion
- D. Oscillatory motion
Answer: C. Circular motion — The Earth orbits the Sun in a nearly circular path. Therefore, its motion around the Sun is considered circular motion.
MCQ 18. What instrument is used to measure the speed of a moving vehicle?
- A. Odometer
- B. Barometer
- C. Speedometer
- D. Anemometer
Answer: C. Speedometer — A speedometer is a gauge that measures and displays the instantaneous speed of a vehicle. An odometer measures distance.
MCQ 19. A boy cycles from his home to school, a distance of 3 km, in 15 minutes. What is his speed in km/h?
- A. 12 km/h
- B. 15 km/h
- C. 20 km/h
- D. 45 km/h
Answer: A. 12 km/h — First, convert 15 minutes to hours: 15/60 = 0.25 hours. Then, Speed = Distance / Time = 3 km / 0.25 h = 12 km/h.
MCQ 20. Which of these is not a unit of time?
- A. Second
- B. Kilogram
- C. Hour
- D. Day
Answer: B. Kilogram — Kilogram is the SI unit of mass. Second, hour, and day are all units used to measure time.
How to Use These Solutions
Attempt each question yourself first and only then compare with the worked answer. Marks in the CBSE board exam are awarded for the METHOD as much as the final result, so reproduce the steps rather than memorising the last line. Where a solution states a law, a formula or a definition, learn that wording — examiners look for it.
Related practice for this chapter: chapter MCQs, previous-year questions, revision notes and sample papers.