# Class 6 NCERT Solutions Science Chapter 7 - Motion and Measurement of Distances

## Motion and Measurement of Distances Exercise 85

### Solution 1

Two examples of modes of transport used on land are buses and wheel carts.

Two examples of modes of transport used on water are ships and boats.

Two examples of modes of transport used in air are aeroplanes and helicopters.

### Solution 2

(i) 100 cm

(ii) 5000 m

Concept insight: 1 km = 1000 m

5 km = 1000 5 = 5000 m

Hence, the answer is 5000 m.

(iii) Periodic motion

Concept insight: The motion of a swing repeats itself after regular intervals of time. Therefore, it has periodic motion. Hence, a child on a swing is said to have periodic motion.

(iv) Periodic motion

Concept insight: The needle of a sewing machine moves up and down repeatedly after regular intervals of time. Hence, it is an example of periodic motion.

(v) Rotational as well as rectilinear

Concept insight: Motion of wheel of a bicycle is rotational as well as rectilinear because the wheel rotates on its axle and also moves forward in a straight line path.

### Solution 3

The size of the footstep varies from person to person. If footsteps of two persons are used to measure the length respectively, then the two distances may not be equal. Thus, a footstep is not a constant quantity. Hence, it cannot be used as a standard unit of length.

Concept insight: Pace and footsteps vary from person to person, so for proper measurements S.I. units have been developed which have a fixed value and are recognized all over the world.

### Solution 4

1 cm = 10 mm

1 m = 100 cm = 1000 mm

Again, 1 km = 1000 m = 100000 cm = 10000000 mm.

Hence, 1 mm is smaller than 1 cm, 1 cm is smaller than 1 m, and 1 m is smaller than 1 km, i.e.,

1 millimetre < 1 centimetre < 1 metre < 1 kilometre

### Solution 5

Height of the person = 1.65 m

1 m = 100 cm

1.65 m = (100 × 1.65) cm = 165 cm

Hence, the height of the person is 165 cm.

Again, 1 m = 100 cm = 1000 mm

Therefore, 1.65 m = 165 cm = (165 × 10) mm = 1650 mm

Hence, the height of the person is 1650 mm.

### Solution 6

The distance between Radha's home and her school is 3250 m.

1 km = 1000 m

i.e., 1 m = km

### Solution 7

The reading of the scale at one end is 3 cm and at the other end is 33. 1 cm.

Therefore, the length of the knitting needle is given by subtracting both the readings, i.e., (33.1- 3.0) cm = 30.1 cm.

### Solution 8

Similarities between the motion of a bicycle and a ceiling fan:

(i) The ceiling fan and the wheels of a bicycle are fixed at a point.

(ii) Both have rotational motion about their respective fixed points.

Difference between the motion of a bicycle and a ceiling fan:

The wheels of a bicycle show rectilinear motion in addition to the rotational motion, while the ceiling fan shows only rotational motion.

### Solution 9

An elastic measuring tape is stretchable. It cannot be used to measure distance because the length of the tape may change on stretching. As a result, the measured length would not be correct.

If we measure a certain distance twice using an elastic tape, then we may get different values for the same length each time. This is because elastic tapes are stretchable.

### Solution 10

Examples of periodic motion:

(i) Motion of a pendulum

The bob of a pendulum repeats its motion regularly after fixed intervals of time. This motion is called periodic motion.

(ii) Motion of a boy sitting on a swing

The motion of a swing repeats itself after regular intervals of time. Hence, a boy sitting on a swing has periodic motion.

Concept insight: A motion which repeats itself regularly after a fixed interval of time is called periodic motion.