Grade 7 Science Ch 13- Motion and Time
Q Fill in the blanks.
i. The metallic ball is called the __________of the pendulum.
ii. The symbols of all units are written in ______________.
iii. The time taken by the pendulum to complete one oscillation is called its ______________.
iv. One microsecond is one ______________of a second.
v. A nanosecond is one ______________of a second.
vi. The distance-time graph for the motion of an object moving with a constant speed is a ___________________.
Q2. True/False
i. The basic unit of time is second. _______
ii. Every object moves with a constant speed. ________
iii. Distances between two cities are measured in kilometres. ________
iv. The time period of a given pendulum is not constant. ________
v. The speed of a train is expressed in m/h. _________
vi. Clocks that measure such small time intervals are used for scientific research. _______
Q3. What is the basic unit of time?
Q4. What is the basic unit of speed?
Q5. What is speedometer?
Q6. What is distance-time graph?
Q7. What is speed?
Q8. What is oscillatory motion?
Q9. What is motion?
Q10. What is circular motion?
Q11. Give an example of oscillatory motion.
Q12. What is non-uniform motion?
Q13. What is uniform motion?
Q14. What is the smallest time interval that can be measured with commonly available clocks and watches?
Q15. What is a simple pendulum?
Q16. How time was measured when pendulum clocks were not available?
Q17. What are quartz clocks?
Q18. What is average speed?
Q19. The distance between two stations is 240 km. A train takes 4 hours to cover this distance. Calculate the speed of the train.
Q20. A simple pendulum takes 32 s to complete 20 oscillations. What is the time period of the pendulum?
Q21. 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.
Q22. When pendulum is said to have one complete oscillation?
Q23. The following Fig. shows the distance-time graph for the motion of two vehicles A and B. Which one of them is moving faster?
Q24. Classify the following as motion along a straight line, circular or oscillatory motion:
(i) Motion of your hands while running. ________________
(ii) Motion of a horse pulling a cart on a straight road. ______________
(iii) Motion of a child in a merry-go-round. ____________________
(iv) Motion of a child on a see-saw. ______________________
(v) Motion of the hammer of an electric bell. __________________
(vi) Motion of a train on a straight bridge. _____________________
Q25. 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.
Q26. Show the shape of the distance-time graph for the motion in the following cases:
(i) A car moving with a constant speed.
(ii) A car parked on a side road.
Q27. 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. Calculate the total distance covered by the car.
Q28. Explain how in ancient time a day, a month and a year were measured?
Q29. What are the points that should be considered while choosing the most suitable scale for drawing a graph?
Q30. Write down the steps to draw a graph.
Q31.Differentiate between distance and displacement.
Q32.Differentiate between uniform speed and average speed.
Q33.How can you say that motion and rest are relative?
Q34.Give an example when objects undergo combinations of different types of motion?
Q35.State different types of motion?
Q36. Look at the graph below of two vehicles A and B, which one of them is moving faster.
Q37. Which of the following distance-time graphs shows a truck moving with speed which is not constant?
Answers
i. The metallic ball is called the bob of the pendulum.
ii. The symbols of all units are written in singular. iii. The time taken by the pendulum to complete one oscillation is called its time period.
iv. One microsecond is one millionth of a second.
v. A nanosecond is one billionth of a second.
vi. The distance-time graph for the motion of an object moving with a constant speed is a straight line.
Q2. True/False
i. The basic unit of time is second. True
ii. Every object moves with a constant speed. False
iii. Distances between two cities are measured in kilometres. True
iv. The time period of a given pendulum is not constant. False
v. The speed of a train is expressed in m/h. False
vi. Clocks that measure such small time intervals are used for scientific research. True
Q3. What is the basic unit of time?
Ans. The basic unit of time is a second. Its symbol is s.
Q4. What is the basic unit of speed?
Ans. Basic unit of speed is metre per second (m/s).
Q5. What is speedometer?
Ans. Speedometer is an instrument that indicates the speed of a vehicle.
Q6. What is distance-time graph?
Ans. Distance-time graph represents the speed of an object.
Q7. What is speed?
Ans. The distance moved by an object in a unit time is called its speed.
Q8. What is oscillatory motion?
Ans. The to and fro motion of an object is called oscillatory motion.
Q9. What is motion?
Ans. Motion is a change in position of an object over time.
Q10. What is circular motion?
Ans. Circular motion is rotation of an object along a circular path
Q11. Give an example of oscillatory motion.
Ans. The to and fro motion of a simple pendulum is an example of a periodic or an oscillatory motion.
Q12. What is non-uniform motion?
Ans. If the speed of an object moving along a straight line keeps changing, its motion is said to be non-uniform.
Q13. What is uniform motion?
Ans. An object moving along a straight line with a constant speed is said to be in uniform motion.
Q14. What is the smallest time interval that can be measured with commonly available clocks and watches?
Ans. The smallest time interval that can be measured with commonly available clocks and watches is one second.
Q15. What is a simple pendulum?
Ans. A simple pendulum consists of a small metallic ball or a piece of stone suspended from a rigid stand by a thread. The metallic ball is called the bob of the pendulum.
Q16. How time was measured when pendulum clocks were not available?
Ans. Many time measuring devices were used in different parts of the world before the pendulum clocks became popular. Sundials, water clocks and sand clocks are some examples of such devices.
Q17. What are quartz clocks?
Ans. Nowadays most clocks or watches have an electric circuit with one or more cells. These clocks are called quartz clocks. The time measured by quartz clocks is much more accurate than that by the clocks available earlier.
Q18. What is average speed?
Ans. Speed or average speed is the total distance covered divided by the total time taken. Thus,
Q19. The distance between two stations is 240 km. A train takes 4 hours to cover this distance. Calculate the speed of the train.
Ans. Distance between two stations = 240 km
Time taken to cover this distance = 4 hours
Q20. A simple pendulum takes 32 s to complete 20 oscillations. What is the time period of the pendulum?
Ans. Number of oscillations = 20
Total time taken to complete 20 oscillations = 32 s
Q21. 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.
Ans. Time taken = 15 min = 15 x 60 = 900 seconds
Speed = 2 m/s
Distance = Speed x Time
= 2 x 900 = 1800 m = 1800/1000 = 1.8 km
Q22. When pendulum is said to have one complete oscillation?
Ans. The pendulum is said to have completed one oscillation when its bob, starting from its mean position B, moves to A, to C and back to B.
Q23. The following Fig. shows the distance-time graph for the motion of two vehicles A and B. Which one of them is moving faster?
Ans. Vehicle A is moving faster. Speed of the vehicle is greater if it covers maximum distance in a given interval of time.
Q24. Classify the following as motion along a straight line, circular or oscillatory motion:
(i) Motion of your hands while running. Oscillatory motion
(ii) Motion of a horse pulling a cart on a straight road. Straight line
(iii) Motion of a child in a merry-go-round. Circular motion
(iv) Motion of a child on a see-saw. Oscillatory motion
(v) Motion of the hammer of an electric bell. Oscillatory motion
(vi) Motion of a train on a straight bridge. Straight line
Q25. 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.
Ans. Distance covered = 57336-57321 = 15 km
Time taken = 8:50 – 8:30 = 20 min
Now, convert 20 min into hour = 20/60 = 1/3 h
Q26. Show the shape of the distance-time graph for the motion in the following cases:
(i) A car moving with a constant speed.
(ii) A car parked on a side road.
Ans. A car moving with a constant speed.
A car parked on a side road.
Q27. 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. Calculate the total distance covered by the car.
Ans. Case 1
Speed = 40km/h
Time taken = 15 min = 15/60 = ¼ hours
Distance = Speed x Time = 40 X ¼ = 10 km
Case 2
Speed = 60km/h
Time taken = 15 min = 15/60 = ¼ hours
Distance = Speed x Time = 60 X ¼ = 15 km
Total Distance = 10 km + 15 km = 25 km
Q28. Explain how in ancient time a day, a month and a year were measured?
Ans. Our ancestors noticed that many events in nature repeat themselves after definite intervals of time. For example, they found that the sun rises every day in the morning. The time between one sunrise and the next was called a day. Similarly, a month was measured from one new moon to the next. A year was fixed as the time taken by the earth to complete one revolution of the sun.
Q29. What are the points that should be considered while choosing the most suitable scale for drawing a graph?
Ans. Some of the points to be kept in mind while choosing the most suitable scale for drawing a graph are:
i. the difference between the highest and the lowest values of each quantity.
ii. the intermediate values of each quantity, so that with the scale chosen it is convenient to mark the values on the graph, and
iii. to utilise the maximum part of the paper on which the graph is to be drawn.
Q30. Write down the steps to draw a graph.
Ans. Steps
i. Draw two perpendicular lines to represent the two axes and mark them as OX and OY.
ii. Decide the quantity to be shown along the x-axis and that to be shown along the y-axis.
iii. Choose a scale to represent the distance and another to represent the time on the graph.
iv. Mark values for the time and the distance on the respective axes according to the scale you have chosen.
v. Mark the points on the graph paper to represent each set of values for distance and time. Join the points.
Q31.Differentiate between distance and displacement.
A- The distance covered by a moving object is the actual length of the path followed by the object is called. Distance is a scalar quantity. SI unit of distance is meter. But Displacement is the shortest distance covered by a moving object from the point of reference (initial position of the body), in a specified direction.
A- An object is said to be moving with uniform speed if it covers equal distances in equal intervals of time. But when we travel in a vehicle the speed of the vehicle changes from time to time depending upon the conditions existing on the road. In such a situation, the speed is calculated by taking the ratio of the total distance travelled by the vehicle to the total time taken for the journey. This is called the average speed.
Q33.How can you say that motion and rest are relative?
A-We have observed that the position of stars and planets change while you remain stationary. In reality the earth is moving too. Thus, an object which appears to be at rest, may actually be in motion. Therefore, motion and rest are relative terms.
Q34.Give an example when objects undergo combinations of different types of motion?
A- The motion of a ball on the ground. Here the ball is rolling on the ground and rotating as well as moving forward on the ground. Thus, the ball undergoes a rectilinear motion as well as rotational motion.
Q35.State different types of motion?
A- Following are different types of motion:
Translatory Motion: - In Translatory motion the particle moves from one point in space to another. This motion may be along a straight line or along a curved path.
Rectilinear motion : Motion along a straight line is called rectilinear motion. Example: A car moving on a straight road
Curvilinear motion: Motion along a curved path is called curvilinear motion. Example: A car negotiating a curve
Rotatory Motion : In rotatory motion, the particles of the body describe concentric circles about the axis of motion
Vibratory Motion: In vibratory motion the particles move to and fro about a fixed point.
Q36. Look at the graph below of two vehicles A and B, which one of them is moving faster.
Ans:
The vehicle A is moving faster as distance represented by vertical axis of A is more as compare to B for a given point of time.
Q37. Which of the following distance-time graphs shows a truck moving with speed which is not constant?
Ans-
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