NCERT Solutions Class 11 Physics - Solved Exercise Question 2.1

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–-1 covers....m in 1 s
(d) The relative density of lead is 11.3. Its density is ....g cm–-3 or ....kg m–-3

Solution:

(a) 1 cm = 1 / 100 m

Volume of the cube = 1 cm3
But, 1 cm3 = 1 cm × 1 cm × 1 cm = (1/100) m X (1/100) m X (1/100) m
∴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
∴ S = 2 X 3.14 X 20 X (20 + 100) = 15072 = 1.5 X 104 mm2

(c) Using the conversion,
1 km/h = (5/18) m/s
18 km/h = 18 X (5/18) = 5 m/s
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 substance / Density of water
= 11.3 X 1 = 11.3 g/cm3
Again, 1g = 1/1000 kg
1 cm3 = 10–6 m3
1 g/cm3 = 10-3 / 10-6 kg m-3 = 103 kg m-3
∴ 11.3 g/cm3 = 11.3 × 103 kg/m3

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