CBSE Class 7 Science Advanced Physics Measurements MCQs Set 03

Answer: (a) Both A and R are true, and R is the correct explanation of A.

Explanation:
1. Weight = mass × acceleration due to gravity (W = mg).
2. The value of g becomes smaller as altitude increases, so the weight of the same body also changes.
3. Both A and R are true, and R explains A, so the answer is (a).

Teacher's Note:
1. Mass stays the same at all heights; only the weight changes.
2. R gives the exact reason why A happens, so option (a) fits.

Answer: (a) Both A and R are true, and R is the correct explanation of A.

Explanation:
1. Volume of the 3 cm cube = 27 cm³ and volume of the 2 cm cube = 8 cm³.
2. A completely immersed solid displaces liquid equal to its own volume, so the 3 cm cube displaces more liquid, and A is true.
3. R states the general rule that explains A, so both are true and R is the correct explanation: (a).

Teacher's Note:
1. Work out both volumes first; 27 cm³ is more than 8 cm³.
2. R is the rule and A is one example of it.

Answer: (c) A is true, but R is false.

Explanation:
1. For equal volumes, the body with the greater density has the greater mass (mass = density × volume).
2. Iron is denser than wood, so 150 m³ of iron has more mass than 150 m³ of wood. A is true.
3. R says iron has less density than wood, which is false. So A is true but R is false: (c).

Teacher's Note:
1. Equal volumes: more density means more mass.
2. Check R against what you know: iron sinks in water while wood floats.

Answer: (d) A is false, but R is true.

Explanation:
1. The numbers for mass (in g) and volume (in cm³) are equal only when the density is 1 g cm⁻³, as for water. For other liquids they are not equal, so A is false.
2. Density = mass ÷ volume, not mass × volume, so R is false.
3. Both A and R are false: (d).

Teacher's Note:
1. Check the formula first: density is a ratio, not a product.
2. Only water has equal numerical mass (g) and volume (cm³).