NCERT Solutions Class 11 Physics - Solved Exercise Question 2.2

Question 2.2:

Fill in the blanks by suitable conversion of units
(a) 1 kg m2 s–-2 = ....g cm2 s–-2
(b) 1 m = ..... ly
(c) 3.0 m s–-2 = .... km h-2
(d) G = 6.67 × 10–11 N m2 (kg)–-2 = .... (cm)3 s-2 g-1.

Solution:

(a) 1 kg = 103 g
1 m2 = 104 cm2
1 kg m2 s–2 = 1 kg × 1 m2 × 1 s–2
=103 g × 104 cm2 × 1 s–2 = 107 g cm2 s–2

(b) Light year is the total distance travelled by light in one year.
1 ly = Speed of light × One year
= (3 × 108 m/s) × (365 × 24 × 60 × 60 s)
= 9.46 × 1015 m
∴ 1 m = 1 / (9.46 X 1015)  = 1.057 X 10-16 ly

(c) 1 m = 10–3 km
Again, 1 s = 1 /3600 h
1 s–1 = 3600 h–1
1 s–2 = (3600)2 h–2
∴3 m s–2 = (3 × 10–3 km) × ((3600)2 h–2) = 3.88 × 104 km h–2

(d) 1 N = 1 kg m s–2
1 kg = 10–3 g–1
1 m3 = 106 cm3
∴ 6.67 × 10–11 N m2 kg–2 = 6.67 × 10–11 × (1 kg m s–2) (1 m2) (1 s–2)
= 6.67 × 10–11 × (1 kg × 1 m3 × 1 s–2)
= 6.67 × 10–11 × (10–3 g–1) × (106 cm3) × (1 s–2)

= 6.67 × 10–8 cm3 s–2 g–1

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