Exercise Questions and Answers on Motion and Time
1. Classify the following as motion along a straight line, circular or oscillatory motion:
(i) Motion of your hands while running
- Answer: Straight line motion
(ii) Motion of a horse pulling a cart on a straight road
- Answer: Straight line motion
(iii) Motion of a child in a merry-go-round
- Answer: Circular motion
(iv) Motion of a child on a see-saw
- Answer: Oscillatory motion
(v) Motion of the hammer of an electric bell
- Answer: Oscillatory motion
(vi) Motion of a train on a straight bridge
- Answer: Straight line motion
2. Which of the following are not correct?
(i) The basic unit of time is second.
- Answer: Correct
(ii) Every object moves with a constant speed.
- Answer: Not correct
(iii) Distances between two cities are measured in kilometres.
- Answer: Correct
(iv) The time period of a given pendulum is constant.
- Answer: Correct
(v) The speed of a train is expressed in m/h.
- Answer: Not correct (It should be km/h)
3. A simple pendulum takes 32 s to complete 20 oscillations. What is the time period of the pendulum?
- Answer:
Time period = Total time taken / Number of oscillations
Time period = 32 s / 20 = 1.6 seconds
4. The distance between two stations is 240 km. A train takes 4 hours to cover this distance. Calculate the speed of the train.
- Answer:
Speed = Distance / Time
Speed = 240 km / 4 h = 60 km/h
5. The odometer of a car reads 57321.0 km when the clock shows the time 08:30 AM. What is the distance moved by the car, if at 08:50 AM, the odometer reading has changed to 57336.0 km? Calculate the speed of the car in km/min during this time. Express the speed in km/h also.
- Answer:
Distance moved = 57336.0 km – 57321.0 km = 15 km
Time taken = 20 minutes = 20/60 = 1/3 hour
Speed = Distance / Time = 15 km / (1/3 h) = 15 × 3 = 45 km/h
Speed in km/min = 15 km / 20 min = 0.75 km/min
6. Salma takes 15 minutes from her house to reach her school on a bicycle. If the bicycle has a speed of 2 m/s, calculate the distance between her house and the school.
- Answer:
Time = 15 minutes = 15 × 60 = 900 seconds
Distance = Speed × Time = 2 m/s × 900 s = 1800 m = 1.8 km
7. Show the shape of the distance-time graph for the motion in the following cases:
(i) A car moving with a constant speed.
- Answer: A straight, upward sloping line (uniform motion).
(ii) A car parked on a side road.
- Answer: A horizontal line (no movement).
8. Which of the following relations is correct?
(i) Speed = Distance × Time
- Answer: Not correct
(ii) Speed = Distance / Time
- Answer: Correct
(iii) Speed = Time / Distance
- Answer: Not correct
(iv) Speed = Time × Distance
- Answer: Not correct
9. The basic unit of speed is:
(i) km/min
- Answer: Not correct
(ii) m/s
- Answer: Correct
(iii) km/h
- Answer: Not correct
(iv) m/min
- Answer: Not correct
10. A car moves with a speed of 40 km/h for 15 minutes and then with a speed of 60 km/h for the next 15 minutes. The total distance covered by the car is:
(i) 100 km
- Answer: Not correct
(ii) 15 km
- Answer: Not correct
(iii) 25 km
- Answer: Correct
(iv) 10 km
- Answer: Not correct
11. Suppose the two photographs, shown in Fig. 9.1 and Fig. 9.2, had been taken at an interval of 10 seconds. If a distance of 100 metres is shown by 1 cm in these photographs, calculate the speed of the fastest car.
- Answer:
This requires the actual distances in the photographs. Calculate the distance covered by the fastest car in 10 seconds and then use the formula for speed:
Speed = Distance / Time.
12. Fig. 9.15 shows the distance-time graph for the motion of two vehicles A and B. Which one of them is moving faster?
- Answer:
The vehicle with the steeper slope on the distance-time graph is moving faster. Compare the slopes of the lines of vehicles A and B.
13. Which of the following distance-time graphs shows a truck moving with speed which is not constant?
(i) Graph showing a straight line
- Answer: Constant speed
(ii) Graph showing a curve
- Answer: Not constant speed
(iii) Graph showing horizontal line
- Answer: No movement
(iv) Graph showing a zigzag line
- Answer: Not constant speed
Extended Learning Activities and Projects
- Make your own sundial and use it to mark the time of the day at your place.
- Answer: Follow the instructions in the book to create a sundial based on your location’s latitude and use it to observe time by marking the tip of the shadow throughout the day.
- Collect information about time-measuring devices that were used in the ancient times.
- Answer: Research various time-measuring devices such as sundials, water clocks, and sand clocks, including their origin, period of use, units of time measured, and images or drawings if possible.
- Make a model of a sand clock which can measure a time interval of 2 minutes.
- Answer: Construct a simple sand clock using two bottles or glass containers, some sand, and a stopwatch for measuring time. Ensure that it can measure the passage of 2 minutes.
- Measure the time period of a swing.
- Answer: Using a stopwatch, measure the time taken for a swing to complete one full oscillation. Repeat with different people sitting on the swing and compare results.
Questions and Answers on Motion and Time
1. What are the three types of motion?
Answer:
The three types of motion are:
- Rectilinear motion (motion along a straight line)
- Circular motion (motion along a circular path)
- Periodic motion (motion that repeats after regular intervals)
2. How can you identify whether an object is moving slowly or fast?
Answer:
The speed of an object can be determined by the distance it covers in a given time. If an object covers more distance in less time, it is moving faster. If it covers less distance in the same time, it is moving slowly.
3. What is speed?
Answer:
Speed is the distance covered by an object in a unit of time. It is given by the formula:
Speed = Total distance covered / Total time taken
4. What is the unit of speed?
Answer:
The unit of speed is meters per second (m/s). It can also be expressed in kilometers per hour (km/h).
5. What is the difference between uniform and non-uniform motion?
Answer:
- Uniform motion occurs when an object covers equal distances in equal intervals of time, without any change in speed.
- Non-uniform motion occurs when an object’s speed or direction of motion changes over time.
6. How do we measure time without a clock?
Answer:
Time can be measured using natural events such as the position of the sun (day and night cycle), or the phases of the moon. Early humans used sundials, water clocks, and sand clocks for measuring time intervals.
7. What is a simple pendulum?
Answer:
A simple pendulum consists of a small mass (bob) suspended from a rigid stand by a string or rod. It swings to and fro around a fixed position and exhibits periodic motion.
8. What is the time period of a pendulum?
Answer:
The time period of a pendulum is the time taken by the pendulum to complete one full oscillation (back and forth motion).
9. How can you determine the time period of a pendulum?
Answer:
By measuring the time taken for 20 oscillations and dividing it by 20, you can calculate the time period of a pendulum.
10. What is the unit of time?
Answer:
The basic unit of time is the second (s). Larger units of time include minutes (min) and hours (h).
11. What are the different devices used to measure time?
Answer:
Common devices for measuring time include clocks and watches (such as wall clocks, table clocks, and digital clocks), as well as older devices like sundials, water clocks, and sand clocks.
12. What is the relationship between seconds, minutes, and hours?
Answer:
- 1 minute = 60 seconds
- 1 hour = 60 minutes = 3600 seconds
13. What is the formula to calculate speed?
Answer:
The formula to calculate speed is:
Speed = Distance / Time
14. What is the difference between average speed and actual speed?
Answer:
- Average speed is the total distance traveled divided by the total time taken, regardless of the variations in speed during the journey.
- Actual speed refers to the speed of an object at a specific moment in time.
15. What is a distance-time graph?
Answer:
A distance-time graph is a line graph that shows how the distance covered by an object changes with time. It helps in understanding the speed and motion of the object.
16. How do you plot a distance-time graph?
Answer:
To plot a distance-time graph, mark the time on the x-axis and the distance on the y-axis. Then, plot points for each set of distance and time values, and join them with a line.
17. What does a straight line on a distance-time graph indicate?
Answer:
A straight line on a distance-time graph indicates uniform motion, meaning the object is moving with constant speed.
18. How do you calculate the speed from a distance-time graph?
Answer:
To calculate speed from a distance-time graph, find the slope of the graph (change in distance / change in time). The slope represents the speed of the object.
19. What is the purpose of a speedometer?
Answer:
A speedometer is a device used in vehicles to measure and display the speed at which the vehicle is traveling.
20. How is a speedometer different from an odometer?
Answer:
A speedometer measures the current speed of the vehicle, while an odometer measures the total distance traveled by the vehicle.
21. What is a microsecond?
Answer:
A microsecond is one millionth of a second (1/1,000,000 seconds).
22. What is a nanosecond?
Answer:
A nanosecond is one billionth of a second (1/1,000,000,000 seconds).
23. How do we calculate the speed of a ball moving on the ground?
Answer:
The speed of the ball can be calculated by dividing the distance it traveled by the time it took to travel that distance:
Speed = Distance / Time
24. What is the time taken by the Earth to complete one revolution around the Sun?
Answer:
The Earth takes one year (365.25 days) to complete one revolution around the Sun.
25. What is the relationship between time and speed?
Answer:
Time and speed are inversely related when distance is constant. The faster an object moves (higher speed), the less time it takes to cover a given distance.
26. What is periodic motion?
Answer:
Periodic motion is the type of motion that repeats itself after regular intervals of time. Examples include the motion of a pendulum or the Earth’s revolution around the Sun.
27. What is the main advantage of using distance-time graphs?
Answer:
Distance-time graphs provide a visual representation of the motion of an object, helping to easily understand the speed, direction, and variation of motion over time.
28. What is the formula for calculating the distance covered by an object?
Answer:
Distance = Speed × Time
29. How do you measure the time period of a pendulum without a stopwatch?
Answer:
If a stopwatch is not available, a table clock or wristwatch can be used to measure the time period of a pendulum by counting the oscillations over a set period of time.
30. How can you calculate the speed of the bus from its odometer readings?
Answer:
To calculate the speed, find the difference in the odometer readings (distance traveled) over the time interval and then use the formula:
Speed = Distance / Time
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