Physical Quantities and Measurement — Important Questions

0.6 g cm⁻³

Step 1: Given: Mass M = 60 g, Volume V = 100 cm³. Step 2: Formula: Density d = M/V. Step 3: d = 60 g / 100 cm³ = 0.6 g cm⁻³. Step 4: Option B (6) results from dividing 60/10 instead of 60/100 — a calculation error. Step 5: The density of wood (about 0.7 g cm⁻³) confirms our answer is reasonable.

kg m⁻³

Step 1: Density = Mass / Volume. Step 2: S.I. unit of mass is kilogram (kg) and S.I. unit of volume is cubic metre (m³). Step 3: Therefore, S.I. unit of density = kg/m³ = kg m⁻³. Step 4: g cm⁻³ is the CGS unit, not the S.I. unit. Step 5: Mixed units like kg cm⁻³ are not standard units.

1000 kg m⁻³

Step 1: We need to convert 1 g cm⁻³ to kg m⁻³. Step 2: 1 g = 1/1000 kg and 1 cm³ = 1/1000000 m³. Step 3: 1 g/cm³ = (1/1000 kg) / (1/1000000 m³) = 1000000/1000 kg m⁻³ = 1000 kg m⁻³. Step 4: So 1 g cm⁻³ = 1000 kg m⁻³. Step 5: This is an important conversion to remember.

Speed

Step 1: This is the definition of speed. Step 2: Speed = Distance travelled / Time taken. Step 3: Distance (in unit time means time = 1) gives us speed directly. Step 4: Density relates mass and volume — not distance and time. Step 5: The answer is Speed, which tells us how fast or slow a body is moving.