**Motion and Measurement of Distances**

**Question 1.Give two examples, each of modes of transport used on land, water and air.**

**Answer:**

- Land – Bus, car, bicycle.
- Water – Motor-boat, ship.
- Air – Aeroplane, Helicopter.

**Question 2.Fill in the blanks :**

(a) One meter is ______cm.**Answer:**100

(b) Five kilometre is ______ m.**Answer:**5000

(c) Motion of a child on a swing is ______.**Answer:**Periodic motion

(d) Motion of a needle of a sewing machine is ______.**Answer:**Periodic motion

(e) Motion of a wheel of a bicycle is ______.**Answer:**Rotational motion

**Question 3.Why can a pace or a footstep not used as a standard unit of length ?**

**Answer:**

A pace or a footstep cannot be used as a standard unit of length because it is different for different persons. Hence correct measurement cannot be made.

**Question 4.Arrange the following lengths in their increasing magnitude.**

*1 meter, 1 centimeter, 1 kilometer, 1 millimeter.*

**Answer:**

- 1 millimeter
- 1 centimeter
- 1 meter
- 1 kilometer

**Question 5.The height of a person is 1.65 m. Express it into cm and mm.**

**Answer:**

(1) 1 m = 100 cm.

∴ 1.65 = 165 cm.

(2) 1 cm = 10 mm

∴ 165 cm = 1650 mm

Hence height of a person is 165 cm or 1650 mm.

**Question 6.The distance between Radha’s home and her school is 3250 m. Express this distance into km.**

**Answer:**

We know,

1000 m = 1 km

∴ 3250 m = × 3250

. = 3.250 km

Hence the distance between Radha’s home and her school is 3.250 km.

**Question 7.While measuring the length of a knitting needle, the reading of the scale of one end is 3.0 cm and at the other end is 33.1 cm. What is the length of the needle ?**

**Answer:**

Length of the needle = Final reading – Initial reading

= 33. cm – 3.0 cm = 30.1 cm.

**Question 8.Write the similarity and dissimilarity between the motion of a bicycle and a ceiling fan that has been switched on.**

**Answer:**

- Similarity – The motion of wheel of bicycle and ceiling fan switched on are same as both have rotational motion.
- Dissimilarity – Bicycle moves in a rectilinear motion, i.e. in a straight line. A switched on ceiling fan has rotational motion as it moves around about its axis.

**Question 9.Why could you not use an elastic measuring tape to measure distance ? What would be some of the problems you would meet in telling someone about a distance you measured with an elastic tape ?**

**Answer:**

We could not use an elastic measuring tape to measure distance because elastic measuring tape cannot measure correct distance. Because if the elastic measuring tape is stretched more than the distance will be less and if it stretched less than the same distance would be more.

The problems we would meet in telling about the distance we measured with an elastic tape are that the distance would be incorrect and would be different every time measured.

**Question 10.Give two examples of periodic motion ?**

**Answer:**

Examples of periodic motion are :

- Motion of a pendulum.
- Motion of a child on a swing.