Here in this post we provided NCERT Exemplar Problem Class 7 Science Motion and Time Chapter 13 Full Explanation by group of Science Experts. We have provided here each questions answer with reason behind the answer.
Hope it help you!
Motion and Time Class 7 Exemplar full Explanation:
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Multiple Choice Questions
1) Which of the following cannot be used for measurements of time ?
a) A leaking tap.
b) Simple pendulum.
c) Shadow of an object during the day.
d) Blinking of eyes.
Answer:- d) Blinking of eyes.
Blinking of eyes cannot use as measurements of time. As the given other can be used sometime.
2) Two clocks A and B are shown in figure. 13. 1. Clock A has an hour and a minute hand, whereas clock B has an hour hand, minute hand as well as a second hand. Which of the following statement is correct for these clocks?
a) A time interval of 30 seconds can be measured by clock A.
b) A time interval of 30 seconds cannot be measured by clock B.
c) Time interval of 5 minutes can be measured by both A and B.
d) Time interval of 4 minutes 10 seconds can be measured by clock A.
Answer:- c) Time interval of 5 minutes can be measured by both A and B.
As clock A does not have second hand it cannot show time within seconds, thus time interval of 5 minutes can be measured by both hand A and B is correct.
3) Two students were asked to plot a distance – time graph for the motion described by table A and table B.
Table A
Distance
Moved (m) |
0 | 10 | 20 | 30 | 40 | 50 |
Time
(Minutes) |
0 | 2 | 4 | 6 | 8 | 10 |
Table B
Distance Moved (m) |
0 | 5 | 10 | 15 | 20 | 25 |
Time
(Minutes) |
0 | 1 | 2 | 3 | 4 | 5 |
The graph given in figure 13.2 is true for
a) Both A and B.
b) A only.
c) B only.
d) Neither A nor B.
Answer:- a) Both A and B.
Both table are true for the given graph.
4) A bus travels 54 km in 90 minutes. The speed of the bus is
a) 0.6 m/s
b) 10 m/s
c) 5.4 m/s
d) 3.6 m/s
Answer:- b) 10 m/s
54 km = 54000 m and 90 min = 5400 s
S= d/ t is the formula for the speed covered.
Therefore, the answer will be
S= 54000m/ 5400 s
S = 10 m/ s
5) If we denote speed by S, distance by D and time by T, the relationship between these quantities is
a) S = D × T
b) T = S /D
c) S=D/T
d) S=
Answer:- c) S= D/T
6) Observe the figure 13.3
The time period of a simple pendulum is the time taken by it to travel from
a) A to B and back to A.
b) O to A, A to B and B to O.
c) B to A , A to B and B to O.
d) A to B.
Answer:- a) A to B and back to A.
When a Bob travel from A to B and back to A this is the time period of simple pendulum .
7) Fig. 13.4 shows an oscillating pendulum.
Time taken by the Bob to move from A to C is t1 and form C to O is t2 . The time period of this simple pendulum is
- (t1+t2)
- 2( t1+ t2)
- 3( t1+ t2)
- 4 (t1+ t2)
Answer:- d) 4(t1+t2) is the time period for simple pendulum.
8) The correct symbol to represent the speed of an object is
a) 5 m/s
b) 5 mp
c) 5 m / s-1
d) 5 s/m
Answer:- a) 5 m/s
m/s (Metre per second) is the correct symbol of speed.
9) Boojho walks to his school which is at a distance of 3 km from his home in 30 minutes. On reaching he finds that the school is closed and comes back by a bicycle with his friend and reaches home in 20 minutes. His average speed in km/h is
a) 8.3
b) 7.2
c) 5
d) 3.6
Answer:-b) 7.2
Average speed is 7.2 km/h.
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Very Short Answer Questions
10) A simple pendulum is oscillating between the A and B as shown in figure 13.5. is the motion of the Bob uniform or non – uniform?
Answer:-A simple pendulum is oscillating between the A and B as shown in figure 13.5 is the Non- uniform motion. Because , when the speed of an object moving along a straight line is changing all the time then it’s motion is said to be Non- uniform motion. Here the given pendulum has the same reason it’s Bob is moving with contact speed over long duration of time therefore it is a Non uniform motion.
11) Paheli and boojho have to cover different distance to reach their school but they take the same time to reach the school. What can you say about their speed ?
Answer:- As paheli and boojho have to cover different distance but both cover them in same time that means their speed is not same. As speeds are different they can cover the different distance in same time.
12) If boojho covers a certain distance in one hour and paheli covers the same distance in two hours, who travels in a higher speed?
Answer:- Boojho covers the same distance in hour which is covered by paheli in two hours thus it is clear that boojho travels with the higher speed than paheli.
• Short Answer Questions
13) Complete the data of the table given below with he help of the distance time graph given in figure 13.6.
Distance
(m) |
0 | 4 | ? | 12 | ? | 20 |
Time
(S) |
0 | 2 | 4 | ? | 8 | 10 |
Answer:-
Distance
(m) |
0 | 4 | 8 | 12 | 16 | 20 |
Time
(s) |
0 | 2 | 4 | 6 | 8 | 10 |
14) The average age of children of class VII is 12 years and 3 months Express this age in seconds.
Answer:-
The average age of the children in class VII is 12 years and 3 months
Therefore
= 12 ×365 + 3×30
= 4470 days.
= 4470 × 24 × 60 × 60 s = 386208000 s
Thus, the age in seconds of the children is 386208000 s.
15) A spaceship travel 36,000 km in one hour. Express its speed in km/s.
Answer:- 1 hour = 60 min= 3600 s
Speed= total distance covered / Total time taken
Speed= 36000 km / 3600 s
Speed of spaceship = 10 km/ s
16) Starting from A, paheli moves along a rectangular path ABCD as shown in figure 13.7. she takes 2 minutes to travel each side. Plot a distance-time graph and explain whether the motion is uniform or non- uniform.
Answer:- As paheli travelled the rectangular path with 2 minutes per side. The motion of paheli is Non-uniform motion. Because the distance covered by paheli per unit time for the total distance covered was not same.
Distance- time Graph is given below:
17) Plot a distance – time graph of the tip of the second hand of a clock by selecting 4 points on x- axis and y- axis respectively. The circumference of the circle traced by the second hand is 64 cm.
Answer:-
Time (s) | X | 15 | 30 | 45 | 60 |
Distance (cm) | Y | 16 | 32 | 48 | 64 |
Graph:-
• Long Answer Questions
18) Given below as figure 13.8 is the distance – time graph of the motion an object.
i) What will be the position of the object at 20s?
Answer:- the position of an object will be 8 m form staring point.
ii) what will be the distance travelled by the object in 12s?
Answer:- The distance travelled by the object in 12 s will be 6 m .
iii) What is the average speed of the object?
Answer:- the average speed of the object will be 0.4 m/s.
19) Distance between bholu’s and Golu’s house is 9 km. Bholu has to attend Golu’sbirthday party at 7 o’clock. He started from his home at 6 o’clock on his bicycle and covered a distance of 6 km in 40 minutes. At the point he met chintuand he spoke to him for 5 minutes and reached Golu’s birthday party at 7 o’clock. With what speed did he cover the second part of the journey? Calculate his average speed for the entire journey.
Answer:- The speed of bholu for the second part of the journey is
Speed = distance covered/ time taken
Speed = 6 km / 40 min
= 6 km/ 0.6666 hr
Speed = 12 km/ hr .
The speed for the second part of the journey is 12 km/ hr.
The average speed of the entire journey
S= D/ T
S= 9 km/ 55 min
S= 9 km/ 0.9166 hr
S= 9.89 km/ hr.
The average speed is Speed= 9 km / hr approximately.
20) Boojho goes to the football ground to play football. The distance time graph of his journey from his home to the ground is given as figure. 13.9.
a) What does the graph between point B and C indicate about the motion of boojho ?
Answer:- the graph between B and C indicate that the motion of boojho is at rest. His speed is zero at that point.
b) Is the motion between 0 to 4 minutes uniform or non- uniform?
Answer:- the motion between 0 to 4 minutes is Non- uniform.
c) What is his speed between 8 and 12 minutes of his journey?
Answer:- the speed between 8 and 12 minutes of his journey is 18.75 m / minute.