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Question 2.1:

Fill in the blanks

(a) The volume of a cube of side 1 cm is equal to.....m3

(b) The surface area of a solid cylinder of radius 2.0 cm and height 10.0 cm is equal to ... (mm)2

(c) A vehicle moving with a speed of 18 km h–1covers....m in 1 s

(d) The relative density of lead is 11.3. Its density is ....g cm–3or . ...kg m–3.

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(a) 1 cm =

a) 1 cm =

Volume of the cube = 1 cm3

But, 1 cm3 = 1 cm × 1 cm × 1 cm =

∴1 cm3 = 10–6 m3

Hence, the volume of a cube of side 1 cm is equal to 10–6 m3.

(b) The total surface area of a cylinder of radius r and height h is

S = 2πr (r + h).

Given that,

r = 2 cm = 2 × 1 cm = 2 × 10 mm = 20 mm

h = 10 cm = 10 × 10 mm = 100 mm

= 15072 = 1.5 × 104 mm2

(c) Using the conversion,

1 km/h =

Therefore, distance can be obtained using the relation:

Distance = Speed × Time = 5 × 1 = 5 m

Hence, the vehicle covers 5 m in 1 s.

(d) Relative density of a substance is given by the relation,

Relative density =

Density of water = 1 g/cm3

Again, 1g =

1 cm3 = 10–6 m3

1 g/cm3 =

∴ 11.3 g/cm3 = 11.3 × 103 kg/m3

Question 3.1:

In which of the following examples of motion, can the body be considered approximately a point object:

(a) a railway carriage moving without jerks between two stations.

(b) a monkey sitting on top of a man cycling smoothly on a circular track.

(c) a spinning cricket ball that turns sharply on hitting the ground.

(d) a tumbling beaker that has slipped off the edge of a table.

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Answer: (a), (b)

(a) The size of a carriage is very small as compared to the distance between two stations. Therefore, the carriage can be treated as a point sized object.

(b) The size of a monkey is very small as compared to the size of a circular track. Therefore, the monkey can be considered as a point sized object on the track.

Question 3.1:

In which of the following examples of motion, can the body be considered approximately a point object:

(a) a railway carriage moving without jerks between two stations.

(b) a monkey sitting on top of a man cycling smoothly on a circular track.

(c) a spinning cricket ball that turns sharply on hitting the ground.

(d) a tumbling beaker that has slipped off the edge of a table.

• Answer

• Discussion

• Share

Answer: (a), (b)

(a) The size of a carriage is very small as compared to the distance between two stations. Therefore, the carriage can be treated as a point sized object.

(b) The size of a monkey is very small as compared to the size of a circular track. Therefore, the monkey can be considered as a point sized object on the track.