**DAV Class 7 Science Chapter 6 Motion and Time Question Answer Notes**

DAV Class 7 Science Chapter 6 Motion and Time Question Answer Notes Solution by Expert Science Teacher. DAV Class 7 Science 6^{th} Chapter Motion and Time for Students of DAV Schools.

**Lesson No 6**

**Motion and Time**

**A.) Fill in the blanks.**

Answer: (1) does not (2) second (3) circular (4) non uniform or linear (5) km/h

**B.) Write True or False for the following statements.**

Answer: (1) False, it is measured in km/hr (2) True (3) False, No he walks 60m (4) False, it does not cover regularly increasing distance (5) True (6) True

**C.) Tick the correct option.**

Answer:

1.) distance = speed x time

2.) 30 minutes

3.) 15 km

4.) option (a)

5.) 4 (t1+t2)

6.) m/second

**D.) Answer the following questions in brief.**

**Q.) 1.) A boy walks to his school with a constant speed of 4 km/h and reaches there in 30 minutes. Find the distance of the school from his house.**

Answer: Speed of the boy is 4 km/h

Time Taken: 30 minutes

Therefore,

Distance of the school from his house = 4 km/h × 30 minutes = 120 km

**Q.) 2.) The distance between two stations is 216 km. A bus takes 4 hours to cover this distance. Calculate the average speed of the bus in km/hour.**

Answer: The distance between two stations = 216 km

Time Taken by the Bus = 4 Hours

Average speed = Distance / Time = 216 km / 4 hours = 54 km/hour

**Q.) 3.) Two Cars, A and B. (starting, at the same time, from the same point) are moving with average speeds of 40 km/h and 50 km/h, respectively, in the same direction. Find how far will Car B be from Car A after 3 hours.**

Distance traveled by Car A = 40 km/h × 3 hours = 120 km

Distance traveled by Car B = 50 km/h × 3 hours = 150 km

Distance between Car A and Car B after 3 hours = 150 km – 120 km = 30 km

**Q.) 5.) Define the term ‘Periodic motion. Give two examples of periodic motions that can be used to measure time.**

Any kind of motion that takes place at regular intervals of time is known as periodic motion.. Rotation of earth around its axis as well as a simple pendulum in motion are two such examples.

**Q.) 6.) Distinguish between uniform and non-uniform motion. Give one example of each.**

Answer:In uniform motion an object travels equal distance in equal amount of time and moves in a straigh line Whereas in non uniform motion an object does not cover equal distance in equal intervals of time.

**Q.) 7.) Draw the shape of distance-time graph for:**

(a.) a man, waiting for a bus, standing at one point, on a bus-stand.

b.) a man, walking on a level, straight and narrow road, with a constant speed.

**E.) Answer the following questions. **

**1.) A farmer moves along the boundary of a rectangular field ABCD as shown in the figure. He takes 4 minutes to travel across each side. Is the motion of this farmer uniform or non uniform? Find his average speed over one complete round of the field**

**2.) During rainy season Shivam noted that the thundering sound of clouds was heard 6 seconds after lightning was seen by him. If the speed of sound in air is 340 meter per second, find the distance of the point where the thundering sound was produced**

**3.) how can we make a simple pendulum A simple pendulum takes 10 seconds to complete 5 oscillations. Find the time period of this pendulum**

Answers

1.) Average speed of the farmer = total distance covered/time taken

= 240 m/16 min.

= 240 m / 960 seconds

= 0.25 m/s

Motion of the farmer is non uniform

2.) Speed at which sound travels= 340 m/s

Time duration = 6 seconds

distance = speed x time = 340 m/s x 6 seconds

= 2040 m

= 2.04 km

3.) Number of complete oscillations = 5

Total time taken = 10 seconds

Time period = Total time/ No of oscillations= 10/5 = 2 seconds

**4.) Carefully examine the data given below for motion of two different objects A and B. State whether the motion of these two objects is uniform or non uniform motion**

TIME | 7:00 a.m | 7:30 a.m | 7:45 a.m | 8:00a.m | 8;15 a.m | 8:30 a.m |

Total distance covered by A (in metres) | 0 | 20 | 30 | 40 | 50 | 60 |

Distance covered by B (in metres) | 0 | 10 | 24 | 35 | 38 | 43 |

Answer- Object A is moving uniformly because it travels the same distance in the same amount of time.

Due to its non-uniform motion, object B does not travel the same distance in the same amount of time.

**5.) Observe the graph and from the graph find – (i) the values of distances P , Q in metre and (ii) the value of time ‘R’ in seconds.**

Distance (m) | 0 | P | 6 | 9 | Q | 15 |

Time (sec) | 0 | 4 | 8 | R | 16 | 20 |

Answer :

(1.) ‘P’ = 3 m, ‘Q’ = 12 m

(2.) ‘R’ = 12 seconds

**More Extra Questions for Preparation**

__Q.1) Fill in the blanks.__

1.) The objects moving along a straight path is called as __linear motion__.

2.) Speed of light in air is __3____×____10 ^{8 }m/s__

**.**

3.) SI unit of speed is __metre per second__.

4.) The simple pendulum was discovered by** Galileo.**

__Q.2) Define the following terms.__

**1.) Speed.**

Answer=Speed is a measure of how fast an object is moving.

**2.) Time.**

Answer=Any change or movement which takes place in terms of a physical dimension called time.

**3.) Periodic event.**

Answer=An event that repeats itself over a regular interval of time is known as a periodic event.

**Q.3.) True or false.**

**1.) All motion is relative.**

Answer= True

**2.) The time interval between one sunrise and the next was called a day.**

Answer=True

**3.) Periodic events are used for measurement of speed.**

Answer=False

**Q.4.) Write the formula of following.**

**1.) Speed**

Answer= speed= distance per unit time

**Q.5) Explain the following.**

**1.) Uniform and non-uniform motion.**

Answer= Uniform motion- An object when it moves along a straight path and covers equal distances in equal intervals of time is called as uniform motion.

Non – uniform motion- When an object does not move along a straight path and time keeps changing is called as non-uniform motion.

**2.) The simple pendulum.**

Answer=

1.) The simple pendulum is made up of a metal ball attached to a taut light string or thread that is fixed rigidly at one end.

2.)The bob of the pendulum is free to oscillate.

3.) When the pendulum is at rest,it is in its mean position.

4.) When the bob of the pendulum is slightly displaced from its mean position, the bob undergoes a regular “to and fro” motion.

5.) One such complete “to and fro” motion is equivalent to one oscillation of the pendulum.

6.) The time taken for one complete oscillation by the pendulum is known as the time period of the pendulum.

**Q.6) Solve the following.**

**1.) The distance from home to school of a boy is 70 km. A bus travels at an average speed of 40 km/h. How much time would it take to travel from home to school?**

Answer=

**Time taken = distance covered / Speed**

= 70 km / 40 km/ h

= 1.75 h

**Q.7) How time was measured when there were no clocks?**

Answer= When there were no clocks the time was measured by sunrise or sunset, sand clocks and water clocks were used.

**Q.8) Explain X-axis and Y- axis on graph.**

Answer= On linear graph, X- axis is used as the time axis (independent variable), and Y- axis is used as distance axis(dependent variable).

** **

**Q.9.) Multiple choice questions.**

**1.) Formula for distance.**

a) Distance= speed/time

b) Distance= speed× time

c) Distance= speed – time

d) None of these

Answer= b) Distance= speed× time

**2.) On which axis is independent variable dependent?**

a) X- axis

b) Y- axis

c) Both a and b

d) None of these

Answer= a) X- axis

**3.) The distance travelled by vehicle is measured by **

a) Thermometer

b) Speedometer

c) Odometer

d) Spectrometer

Answer= c) Odometer

**4.) Distance is measured in**

a) km

b) cm

c) m

d) mm

Answer= a) km

**5.) The basic unit of speed is **

a) km/s

b) cm/s

c) m/s

d) None of these

Answer= c) m/s