# Motion and Measurement

## NCERT Solution

#### Fill in the blanks:

- One metre is ______________ cm.

**Answer:** 100
- Five kilometre is ______________ m.

**Answer:** 5000
- Motion of a child on a swing is ______________.

**Answer:** Periodic motion
- Motion of the needle of a sewing machine is ______________.

**Answer:** Periodic motion
- Motion of wheel of a bicycle is______________.

**Answer:** Circular motion

## Answer the following questions

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

**Answer:** Land: Bus, Water: Ship and Air: Airplane

Why can a pace or a footstep not be used as a standard unit of length?

**Answer:** Length of footstep can be different for different persons. Using it as a standard unit of length would create confusion. Hence, a pace or a footstep cannot be used as a standard unit of length.

Arrange the following lengths in their increasing magnitude: 1 metre, 1 centimetre, 1 kilometre,1 millimetre.

**Answer:** 1 millimeter < 1 centimeter < 1 meter < 1 kilometer

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

**Answer:** We know that 1 m = 100 cm

Hence, 1.65 m = 1.65 × 100 = 165 cm

Now, 1 cm = 10 mm

Hence, 165 cm = 165 × 10 = 1650 mm

## Answer the following questions

The distance between Radha's home and her school is 3250 m. Express this distance into km.

**Answer:** We know that 1000 m = 1 km

Hence, 1 m = 1 ÷ 1000 m

Hence, 3250 m = (1 ÷ 1000 m) × 3250 = 3.25 km

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

**Answer:** Here; reading at the beginning point = 3.0 cm

Reading at the end point = 33.1 cm

Measurement = Final reading – Initial reading

= 33.1 – 3.0 = 30.1 cm

Write the similarities and differences between the motion of a bicycle and a ceiling fan that has been switched on.

**Answer:** : Similarities: The wheels of the bicycle and the ceiling fan are in circular motion.

Difference: While the bicycle also shows translatory motion, the ceiling fan remains fixed at a place.

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:** An elastic measuring tape is highly flexible and hence it would give different readings at different times. Hence, an elastic measuring tape cannot be used to measure distance.

Give two examples of periodic motion.

**Answer:** Two examples of periodic motion are; motion of the pendulum of a clock and motion of a swing.