Welcome to the complete solutions guide for Class 7 Science Chapter Time and Motion Oxford Solutions aligned with CBSE standards. This chapter introduces students to fundamental concepts of time, speed, motion, and their interrelationships.
Our step-by-step solutions are designed to simplify complex ideas, clarify doubts, and strengthen understanding—helping students prepare effectively for exams. Whether you’re a student, parent, or teacher, these solutions will serve as a reliable companion in mastering this important science topic.
Class 7 Science Chapter Time and Motion Oxford Textbook Answers
I. Objective type questions
A. Fill in the blanks with the correct words.
- A water clock and a sand clock are two examples of ancient (modern/ancient) clocks.
- A sundial works only in the day (day/night).
- In a pendulum, the greater the length of the string, the greater (greater/lesser) is the time period.
II. Multiple Choice Questions
B. Choose the correct option.
- Which of these does not measure time?
- a. Timer
- b. Stopwatch
- c. Measuring tape
- d. Wrist watch
Answer: c. Measuring tape
Reason: A timer, stopwatch, and wrist watch all measure time. A measuring tape is used to measure length or distance.
2. What does one hour equals to?
- a. 60 seconds
- b. 60 weeks
- c. 3600 minutes
- d. 3600 seconds
Answer: d. 3600 seconds
Reason: One hour is equal to 60 minutes, and each minute has 60 seconds.
Therefore, 60minutes×60seconds/minute=3600seconds.
3. Which of these is not related to a pendulum?
- a. Bob
- b. String
- c. Time period
- d. Sundial
Answer: d. Sundial
Reason: A pendulum is a device with a bob (mass) suspended by a string, which swings with a specific time period. A sundial is a time-telling device that uses the sun’s shadow.
4. In which unit is the time period of a pendulum measured?
- a. Days
- b. Metres per second
- c. Seconds
- d. Years
Answer: c. Seconds
Reason: The time period of a pendulum is the time it takes to complete one oscillation, and time is measured in units of seconds.
5. Which of these is correct for a body in uniform motion?
- a. It covers equal distances in unequal intervals of time
- b. It covers unequal distances in equal intervals of time
- c. It covers equal distances in equal intervals of time
- d. Both a and c
Answer: c. It covers equal distances in equal intervals of time
Reason: By definition, uniform motion is when an object travels equal distances in equal intervals of time.
6. What is a sundial used for?
- a. Steering a car
- b. Dialling a telephone number
- c. Measuring time
- d. Measuring speed
Answer: c. Measuring time
Reason: A sundial is an ancient instrument used to measure time based on the position of the sun.
7. What does an hour glass use to measure time?
- a. The angle of the sun
- b. The to and fro motion of a pendulum
- c. The amount of sand streaming down
- d. The angle of the moon
Answer: c. The amount of sand streaming down
Reason: An hourglass measures time by the flow of a fixed amount of sand from one bulb to the other.
8. Under the influence of which of the following does the bob of a pendulum swing?
- a. Time
- b. Gravity
- c. Daylight
- d. Periodic motion
Answer: b. Gravity
Reason: Gravity is the force that pulls the bob of a pendulum back towards its equilibrium position, causing the swinging motion.
9. How much are ten decades equal to?
- a. One millennium
- b. One century
- c. Ten centuries
- d. Ten years
Answer: b. One century
Reason: A decade is 10 years, so ten decades are equal to 10×10=100 years, which is one century.
10. What does the time period of a simple pendulum depend on?
- a. The time of the day
- b. The length of the string
- c. The mass of the bob
- d. The size of the bob
Answer: b. The length of the string
Reason: The time period of a simple pendulum is primarily dependent on the length of its string and the acceleration due to gravity. It does not depend on the mass or size of the bob.
III. Very short answer type questions
Give two examples for the following.
- Units of time smaller than an hour
- Second
- Minute
- Time-measuring instruments in earlier times
- Sundial
- Water clock
- Modern time-measuring instruments
- Digital watch
- Quartz clock
- Factors on which the time period of a pendulum depends
- Length of the string
- Acceleration due to gravity
- Factors on which the time period of a pendulum does not depend
- Mass of the bob
- Amplitude of the oscillation
IV. Short answer type questions
1.What is periodic motion?
Ans: Periodic motion is a motion that repeats itself after equal intervals of time. An example is the motion of a pendulum or the Earth’s revolution around the sun.
2. Name the following.
a) Instrument for measuring speed in an automobile:
Ans: Speedometer.
b) Instrument for measuring distance travelled in an automobile:
Ans: Odometer.
3. What is the time period of a pendulum?
Ans: The time period of a pendulum is the time it takes for one complete back-and-forth swing, or oscillation.
4. What is one oscillation of a pendulum?
Ans: One oscillation is a complete to-and-fro motion of the pendulum bob from one extreme position to the other and back to the starting point.
5. What is average speed?
Ans: Average speed is the total distance an object travels divided by the total time it takes to travel that distance.
V. Long answer type questions
1. Why is the measurement of time important to us?
Ans: Measurement of time is crucial for organizing our lives. It allows us to schedule events, coordinate activities, and understand the duration of processes. Without it, our daily routines and societal functions would be chaotic.
2. How did people in earlier days measure time using the following?
Ans: Sundial: A sundial uses the shadow cast by a vertical rod (gnomon) on a calibrated dial to indicate the time of day. The position and length of the shadow change as the sun moves across the sky.
Hourglass: An hourglass consists of two glass bulbs connected by a narrow neck, containing a specific amount of sand. Time is measured by the amount of time it takes for all the sand to flow from the upper bulb to the lower one.
3. Describe an activity to demonstrate the constancy of the time period of a pendulum.
Ans: Suspend a simple pendulum. Displace the bob slightly and measure the time it takes for 20 oscillations using a stopwatch. Repeat this process with a slightly larger initial displacement. You’ll find that the time for 20 oscillations is nearly the same in both cases, which demonstrates that the time period of a pendulum is constant for small oscillations, irrespective of the amplitude.
4. What is a distance-time graph? How can we find the speed of an object from its distance-time graph?
Ans: A distance-time graph plots the distance traveled by an object on the y-axis against the time taken on the x-axis. The speed of the object can be calculated from the slope of the line. The slope is equal to the change in distance divided by the change in time (speed = distance/time). A steeper slope indicates a higher speed.
5. Distinguish between uniform and non-uniform motion. Also, give examples of each.
Ans: Uniform motion: An object is in uniform motion when it covers equal distances in equal intervals of time. Its speed remains constant.
Example: A car moving at a steady 60 km/h on a straight, empty road.
Non-uniform motion: An object is in non-uniform motion when it covers unequal distances in equal intervals of time. Its speed changes over time.
Example: A bus traveling in city traffic, as it speeds up, slows down, and stops at signals.
VI. Numerical questions
1. Convert the following:
a) 2400 seconds to minutes:
Ans: 2400÷60=40 minutes.
b) 8 hours to minutes:
Ans: 8×60=480 minutes.
c) How many hours are there in 3 days?
Ans: 3days×24hours/day=72 hours.
d) How many days are there in one decade? (Take 365¼ days in each year.
Ans: 10years×365.25days/year=3652.5 days.
e) Calculate the number of minutes in a day.
Ans: 24hours×60minutes/hour=1440 minutes.
f) An object moves 360 km in 2 hours. Calculate its speed in km/h and m/s.
Ans: Speed in km/h: 360km÷2h=180km/h.
Speed in m/s: 180×185=50 m/s.
g) A car covers 240 km in 3 hours and a motorcycle covers 360 km in 4 hours. Which vehicle is travelling faster?
Ans: Car speed: 240km÷3h=80km/h.
Motorcycle speed: 360km÷4h=90km/h.
The motorcycle is traveling faster.
h) Plane ‘A’ travels at 900 km/h and plane ‘B’ travels at 250 m/s. Which plane travels faster?
Ans: Convert Plane B’s speed to km/h: 250m/s×3.6=900km/h.
Both planes travel at the same speed.
j) In a cricket match, on an average, it takes 5 minutes to bowl one over and 1 minute to cross over after each over. How many overs (including the time taken for cross-over) can be finished in 1 hour?
Ans: Time per over (with cross-over): 5+1=6 minutes.
Total time: 1hour=60 minutes.
Number of overs: 60÷6=10 overs.
k) Sonu goes for basketball coaching three times a week, and swimming classes two times a week. Each basketball class is for 1 hour and 45 minutes, and each swimming class is for an hour. How much time does she spend in a week in these two classes?
Ans: Basketball time: 3×(1h+45min)=3h+135min=5h and 15min.
Swimming time: 2×1h=2h.
Total time: 5h+15min+2h=7h and 15min.
l) If you travel by road, it takes 46 hours to travel from New Delhi to Kanyakumari. How many days and hours would this be?
Ans: 46÷24=1 with a remainder of 22.
1Day and 22 hours.
m) Kushal loves to visit his grandparents every year to spend his summer holidays with them. They live in a remote village. He takes a train, then a bus and then, walks the rest of the journey. The train travels at 60 km/h for 5 hours, the bus travels at 40 km/h for 3 hours and he walks at a speed of 5 km/h for 1 hour. What is the total distance he travels from the railway station to his grandparents’ house?
Solution Distance Traveled by Train
- Speed: 60 km/h
- Time: 5 hours
- Distance: Speed × Time = 60km/h×5h=300km
Distance Traveled by Bus
- Speed: 40 km/h
- Time: 3 hours
- Distance: Speed × Time = 40km/h×3h=120km
Distance Traveled by Walking
- Speed: 5 km/h
- Time: 1 hour
- Distance: Speed × Time = 5km/h×1h=5km
Total Distance
- Total Distance: Distance by Train + Distance by Bus + Distance by Walking
- Total Distance: 300km+120km+5km=425km
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