NCERT Exemplar Problems Class 6 Science – Motion and Measurement of Distances

Question 1:
The distance between Delhi and Mumbai is usually expressed in units of
(a) decametre
(b) metre
(c) centimetre
(d) kilometre
Solution:
(d) The distance between Delhi and Mumbai is expressed in kilometre because other units like metre, centimetre and decametre are so small to express this big distance.

Question 2:
Which of the following does not express a time interval?
(a) A day
(b) A second
(c) A school period
(d) Time of the first bell in the school
Solution:
(d) Time of the first bell in the school does not express a time interval because it has only a single value of time, while the other quantities like a day, a second and a school period can be divided into a number of shorter periods of time.
Note: A time interval should have atleast two values of time.

Question 3:
Figure shows a measuring scale which is usually supplied with a geometry box. Which of the following distance cannot be measured with this scale by using it only once?

(a) 0.1 m (b) 0.15 m
(c) 0.2 m (d) 0.05 m
Solution:
(c) Here, 0.1 m = 10 cm
0.15 m = 15 cm [∴ 1 m = 100 cm]
0.2 m = 20 cm and 0.05 m = 5 cm
The distances 10 cm, 15 cm and 5 cm can be easily measured by using a 15 cm long scale, while the distance 20 cm (= 0.2 m) cannot be measured by using this scale only once.

Question 4:
A piece of ribbon folded five times is placed along a 30 cm long measuring scale as shown in figure.

The length of the ribbon is between
(a) 1.15 m-1.25 m
(b) 1.25 m-1.35 m
(c) 1.50 m-1.60 m
(d) 1.60 m-1.70 m
Solution:
(b) Since, ribbon is folded 5 times, i.e. from figure, length of ribbon = (27.5 – 2) cm x 5 = (25.5 x 5) cm
= 127.5 cm = 1.27 m [∴1m = 100 cm]

1.27 m lies in the range of 1.25 m – 1.35 m.

Question 5:
Paheli moves on a straight road from point A to point C. She takes 20 min to cover a certain distance AB and 30 min to cover the rest of distance BC. She then turns back and takes 30 min to cover the distance CB and 20 min to cover the rest of the distance to her starting point. She makes 5 rounds on the road in the same way. Paheli concludes that her motion is
(a) only rectilinear motion
(b) only periodic motion
(c) rectilinear and periodic motion
(d) neither rectilinear nor periodic
Solution:
(c) We can understand this using the following diagram:

Thus, we can see that Paheli moves in a straight path from A ->C and from C -> A. So, the motion is rectilinear, further Paheli moves in a periodic motion because she makes 5 rounds in the same way and crosses point 6 in each round, after a regular time interval. So, her motion is rectilinear and periodic.

Question 6:
Bholu and Golu are playing on a ground. They start running from the same point A in the ground and reach point B at the same time by following the paths marked 1 and 2, respectively as shown in the figure. Which of the following is true for the given situation?

As compared to Golu, Bholu covers a
(a) longer distance but with a lower speed
(b) longer distance with a higher speed
(c) shorter distance with a lower speed
(d) shorter distance with a higher speed
which is longer than that of Golu. Both reaches point B at the same time, so Bholu will have to move faster in order to cover more distance (Golu is on the track having the shortest distance between A and B).Therefore, Bholu moves with a higher speed than Golu.
Solution:
(b) It is clear from the figure that Bholu covers more distance, since he is on the track

Question 7:
Four pieces of wooden sticks A, B, C and D are placed along the length of 30 cm long scale as shown in figure. Which one of them is 3.4 cm in length?

Solution:
(c) From the figure it is clear that,
length of A = (2.7 – 0.3) cm = 2.4 cm,
length of S = (6.5 – 3.4) cm = 3.1 cm
length of C = (10.4 – 7.0) cm = 3.4 cm and
length of D = (14.4 – 10.7) cm = 3.7 cm
So, length of C is same as asked, i.e. 3.4 cm.

Question 8:
Which of the following figure shows the correct placement of a block along a scale for measuring its length?


Solution:
(c) We can see that (a), (b) and (d) have the placement of block which is going out of the marking of 15 cm scale. Only (c) has the placement which is inside the marking of scale.

Question 9:
You are provided three scales A, B and C as shown in figure to measure a length of 10 cm.

For the correct measurement of the length, you will use the scale
(a) only A
(b) only B
(c) only C
(d) Any of the three scales
Solution:
(d) We can see that all the scales have 10 cm length interval on their non-broken sides. So, for scale A, length of interval available = 15 – 3 = 12 cm
For scale B, length of interval available = 15 – 3 = 12 cm
For scale C, length of interval available = 13 – 0 = 13 cm
So, (d) is correct option.

Very Short Answer Type Questions

Question 10:
Correct the following.
(a) The motion of a swing is an example of rectilinear motion.
(b) 1 m = 1000 cm
Solution:
(a) The motion of a swing is an example of periodic motion. Since, it repeats its motion after a regular interval of time.
(b) 1 m = 100 cm [Each metre (m) has hundred equal divisions, called centimetre (cm)]

Question 11:

1. of an object or a part of it around a fixed point is known as ………. motion.
2. A body repeating its motion after certain interval of time is in ………… motion.
3. In rectilinear motion, object moves ………. a ……….. line.
4. The SI unit of length is ……….

Solution:

1. circular
   Note: In circular motion an object moves such that its distance from a fixed point remains the same.
2. periodic, e.g. motion of pendulum of wall clock.
3. along straight, e.g. motion of a vehicle on a straight road. .
4. metre

Question 12:
Give one example for each of the following type of motion.
(a) Rectilinear
(b) Circular
(c) Periodic
(d) Circular and periodic
Solution:
(a) Motion of a stone falling from a height.
(b) Motion of a point marked on blades of a rotating fan.
(c) Motion of moon around the earth.
(d) Motion of hands of a clock.

Short Answer Type Questions

Question 13:
The photograph given in figure shows a section of a grille made up of straight and curved iron bars. How would you measure the length of the bars of this section, so that the payment could be made to the contractor?

Solution:
The length of straight iron bars of grille is measured directly with a measuring tape.
For curved iron bars, the length can be measured using a thread which can be further measured with the help of measuring tape.

Question 14:
Identify the different types of motion in the following word diagram given as in the figure.

Solution:
The different types of motion in the following word diagram is as given:

Question 15:
Four children measure the length of a table which was about 2 m. Each of them used different ways to measure it.
(a) Shyam measured it with a half metre long thread.
(b) Gurmeet measured it with a 15 cm scale from her geometry box.
(c) Reena measured it using her handspan.
(d) Salim measured it using a 5 m long measuring tape.
Which one of them would get the most accurate length? Give reason for your answer.
Solution:
(d) Salim will measure it most accurately because of the following reasons:

1. Length 2 m which he wants to measure can be measured using this scale only in a single attempt.
2. This scale is standard scale and will give the correct measurement.
   Other scales given are either non-standard or having the length less than the length we want to measure.

Question 16:
Match the Column I with Column II.

Solution:
The correct matching is as given (a)-(ii), (b)-(i), (c)-(iii)
(a) Rotational motion is a motion in a circular path about a fixed axis.
(b) Circular motion is a motion of an object or a part of it around a fixed point.
(c) Periodic motion is the motion that repeats itself after some period of time.

Long Answer Type Questions

Question 17:
While travelling in a train, it appears that the trees near the track are moving whereas co-passengers appear to be stationary. Explain the reason.
Solution:
While travelling, trees near the track seem to be moving back (i.e. opposite to the direction of motion of a train) because there is a relative motion between the outside trees and the moving train.
While in case of co-passengers, the relative motion between us and co-passengers, is zero, so they appear to be stationary.

Question 18:
How are the motions of a wheel of a moving bicycle and a mark on the blade of a moving electric fan different? Explain.
Solution:
Differences between wheel of moving bicycle and mark on the blade of electric fan are as given:

Question 19:
Three students measured the length of a corridor and reported their measurements. The values of their measurements were different. What could be the reason for difference in their measurements?
(Mention any three)
Solution:
The reasons may be as follows :

1. Their scales of measurement may not be standard or they may be using different scales of measurement. .
2. The length of the scale may not be proper, i.e. the length of scale may be shorter than the length they want to measure.
3. There may be some errors in the scale which they are using or they may not be using the correct method of observing the scale.

Question 20:
Boojho was riding in his bicycle along a straight road. He classified the motion of various parts of the bicycle as (a) rectilinear motion (b) circular motion and (c) both rectilinear as well as circular motion. Can ‘ you list one part of the bicycle for each type of motion? Support your answer with reason.
Solution:
(a) Rectilinear motion The handle of bicycle will always move in rectilinear path because it cannot execute circular or rotatory motion.
(b) Circular motion The pedals of bicycle will always move circularly around its chain fixing system because they cannot move in forward direction without the whole chain system.
(c) Both rectilinear and circular The wheels of bicycle will move in rectilinear as well as in circular motion because the wheel as a whole will move forward and its point or particles around the rim will execute circular motion.