Verified Solution • 2025–26 Session moderate

Q1.2: NCERT Physics - Part 1 UNITS AND MEASUREMENT 1.2 Solution: Fill in the blanks by suitable conversion of units (a) 1 kg m_…

⚠️ Common Exam Traps & Conceptual Pitfalls

When converting gravitational constant $G$ from SI to CGS, students often forget that $1 \text{ N} = 10^5 \text{ dyn}$, leading to a magnitude error of $10^5$. Always convert the force unit first to ensure the final exponent for $G$ is $10^{-8}$.

Fill in the blanks by suitable conversion of units

(a) 1 kg m_ s__ = ....g cm_ s__

(b) 1 m = ..... ly

(c) 3.0 m s__ = .... km h__

(d) G = 6.67 _ 10___ N m_ (kg)__ = .... (cm)_ s__ g__

Multiple Choice Options

  • A
  • B
  • C
  • D

Step-by-Step Verified Solution

**Answer:**

(a) 10710^7 g cm_ s__

(b) 1.057×10−161.057 \times 10^{-16} ly

(c) 3.888×1043.888 \times 10^4 km h__

(d) 6.67×10−86.67 \times 10^{-8} (cm)_ s__ g__

**Step-by-Step Explanation:**

(a) 1 kg m2 s−2=1000 g×(100 cm)2 s−2=107 g cm2 s−21 \text{ kg m}^2 \text{ s}^{-2} = 1000 \text{ g} \times (100 \text{ cm})^2 \text{ s}^{-2} = 10^7 \text{ g cm}^2 \text{ s}^{-2}.

(b) 1 ly=9.46×1015 m1 \text{ ly} = 9.46 \times 10^{15} \text{ m}. So 1 m=19.46×1015=1.057×10−16 ly1 \text{ m} = \frac{1}{9.46 \times 10^{15}} = 1.057 \times 10^{-16} \text{ ly}.

(c) 3.0 m s−2=3.0×10−3 km×(3600)2 h−2=3.888×104 km h−23.0 \text{ m s}^{-2} = 3.0 \times 10^{-3} \text{ km} \times (3600)^2 \text{ h}^{-2} = 3.888 \times 10^4 \text{ km h}^{-2}.

(d) G=6.67×10−11 N m2 kg−2=6.67×10−11×105 dyn×104 cm2×10−6 g−2=6.67×10−8 (cm)3 s−2 g−1G = 6.67 \times 10^{-11} \text{ N m}^2 \text{ kg}^{-2} = 6.67 \times 10^{-11} \times 10^5 \text{ dyn} \times 10^4 \text{ cm}^2 \times 10^{-6} \text{ g}^{-2} = 6.67 \times 10^{-8} \text{ (cm)}^3 \text{ s}^{-2} \text{ g}^{-1}.

All Questions in this Chapter

Q1.1 Q1.2 Q1.3 Q1.4 Q1.5 Q1.6 Q1.7 Q1.8 Q1.9 Q1.10 Q1.11 Q1.12 Q1.13 Q1.14 Q1.15 Q1.16 Q1.17

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