Q:

A:

- In a simple pendulum, the bob repeats its motion at a certain time interval. This motion is known as periodic motion.
- The motion of a swing repeats its motion at a certain time interval. Thus, a girl sitting on a swing has periodic motion.

Q:

A:

On converting all the given measures in millimetres (mm), we get

1 cm = 10 mm

1 m = 100 cm = 1000 mm

1 km = 1000 m = 100000 cm = 1000000 mm

So, the lengths in increasing order of magnitude can be written as,

1 millimetre < 1 centimetre < 1 metre < 1 kilometre

Q:

A:

Similarities: The blades of the fan and the wheels of the bicycle are attached at a fixed point. Secondly, both have circular motion about their respective fixed points.

Differences: The blades of the fan have circular motion while the bicycle has linear motion. Secondly, the motion of the blades of a fan is periodic while the motion of a bicycle is rectilinear motion.

Q:

A:

Given, reading at one end = 3.0 cm

reading at the other end = 33.1 cm

The length of the knitting needle can be calculated by subtracting 33.1 cm by 3.0 cm.

length of the knitting needle = 33.1 cm – 3.0 cm = 30.1 cm

Hence, the length of the knitting needle would be 30.1 cm.

Q:

A:

\begin{array}{l}\text{Given,thedistancebetweenRadha'shomeandherschool=3250m}\\ \text{As1km=1000m}\\ \text{or1m=}\frac{\text{1}}{\text{1000}}\text{km}\\ \text{Converting3250mintokm,weget}\\ \Rightarrow \text{3250m=3250\xd7}\frac{\text{1}}{\text{1000}}\text{km=3}\text{.25km}\end{array}

Q:

A:

Given, height of the person = 1.65 m

As, 100 cm = 1 m

So, height of the person in cm = 1.65 × 100 cm = 165 cm

Also, 1000 mm = 1 m

So, height of the person in mm = 1.65 × 1000 cm = 1650 mm

Q:

A:

The size of the foot is not same of each person. When footsteps of two people are used to measure the length, the two distances may not be equal. Therefore, footstep is not a constant quantity and cannot be used as a standard unit of length.

Q:

A:

An elastic measuring tape is not a suitable measuring scale because it can be stretched. In this case, the measured length would not be correct. If you measure the length of an object twice using an elastic tape, then you may get different values of the same length.

Q:

A:

__Modes of transport used on land__: Cars and trains

__Modes of transport used on water__: Ships and boats

__Modes of transport used in air__: Airplanes and helicopters

Q:

A:

(i) One metre is __100__ cm.

__Explanation:__ There are 100 cm in 1 m.

(ii) Five kilometres is __5000__ m.

__Explanation:__ There are 1000 m in 1 km.

So, 5 km = 5 × 1000 m = 5000 m

(iii) Motion of a child on a swing is __periodic__.

__Explanation:__ At a certain time interval, the motion of a swing repeats itself. Hence, it is an example of periodic motion.

(iv) Motion of the needle of a sewing machine is __periodic__.

__Explanation:__ The needle of a sewing machine moves up and down frequently in a certain time interval. So, it is an example of periodic motion.

(v) Motion of the wheel of a bicycle is __circular__.

__Explanation:__ The wheel of a bicycle rotates about a fixed point as the bicycle moves. Thus, it is an example of circular motion.

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