Mass and Weight – Long Answer Questions
Medium Level (Application & Explanation)
Q1. Define mass. Explain why mass is constant and how it relates to inertia. Give examples from Earth and Moon.
Answer:
- Mass is the amount of matter in a body.
- It is measured in kilograms (kg).
- Mass is constant. It does not change with place.
- It is the measure of inertia. More mass means more resistance to change in motion.
- A 10 kg block on Earth is still 10 kg on the Moon.
- Mass does not depend on gravity. It depends on how much matter is present.
Q2. What is weight? State its formula and units. Explain why weight changes from place to place.
Answer:
- Weight is the force with which Earth pulls an object.
- It depends on both mass (m) and gravity (g).
- Formula: W = m × g.
- Its SI unit is newton (N).
- Weight changes because g is different at different places.
- On Earth g ≈ 9.8 m/s². On the Moon g is about 1/6th of Earth.
Q3. Differentiate between mass and weight with suitable points and examples.
Answer:
- Mass is amount of matter. Weight is the gravitational force on the object.
- Mass is measured in kg. Weight is measured in N.
- Mass is constant everywhere. Weight changes with g.
- Mass is linked to inertia. Weight is linked to gravity.
- A 5 kg object is 5 kg on Earth and Moon. But its weight is 49 N on Earth and about 8.17 N on Moon.
- Mass is measured with a beam balance. Weight is measured with a spring balance.
Q4. Why is the weight of an object on the Moon about one-sixth of its weight on Earth?
Answer:
- Weight depends on g. So W = m × g.
- The Moon has much less mass than Earth.
- The Moon also has a smaller radius.
- Due to these, the Moon’s gravity is weaker.
- Moon’s g ≈ 1/6th of Earth’s g.
- So for the same mass, weight on Moon becomes about one-sixth of that on Earth.
Q5. Show how W = m × g explains different weights on Earth, Moon, and Mars with calculations.
Answer:
- Take m = 10 kg.
- On Earth: g ≈ 9.8 m/s². So W = 10 × 9.8 = 98 N.
- On Moon: g ≈ 1/6 of Earth ≈ 1.63 m/s². So W = 10 × 1.63 = 16.3 N.
- On Mars: g ≈ 3.7 m/s². So W = 10 × 3.7 = 37 N.
- Mass stays 10 kg everywhere.
- Only g changes, so weight changes.
High Complexity (Analysis & Scenario-Based)
Q6. An astronaut takes a beam balance and a spring balance to the Moon. Both measure a 5 kg block. What readings will each show on Earth and on the Moon? Explain.
Answer:
- On Earth, the beam balance compares masses. It shows 5 kg, as it balances against known masses.
- The spring balance measures weight. On Earth it shows W = 5 × 9.8 = 49 N.
- On the Moon, the beam balance still shows 5 kg. Mass does not change.
- On the Moon, the spring balance shows W ≈ 5 × 1.63 = 8.15 N.
- Reason: beam balance is based on mass comparison.
- Spring balance is based on force and depends on g.
Q7. Two identical 2 kg objects are at sea level and at a high mountain. Compare their mass and weight at both places. Also comment on what happens in the International Space Station (ISS).
Answer:
- At sea level, mass of each is 2 kg. Weight is W = 2 × 9.8 = 19.6 N.
- On a high mountain, mass is still 2 kg.
- Gravity is slightly less at higher altitude.
- So weight becomes a little less than 19.6 N. The change is small.
- In the ISS, mass is still 2 kg.
- Weight becomes near zero due to microgravity, though inertia remains the same.
Q8. A suitcase shows 150 N on a spring scale on Earth. Find its mass. What will be its weight on the Moon and on Mars (g = 3.7 m/s²)? Explain your steps.
Answer:
- On Earth: W = 150 N and g = 9.8 m/s².
- Mass, m = W/g = 150/9.8 ≈ 15.31 kg.
- On the Moon: g ≈ 1.63 m/s². So W = m × g ≈ 15.31 × 1.63 ≈ 24.9 N.
- On Mars: g = 3.7 m/s². So W ≈ 15.31 × 3.7 ≈ 56.6 N.
- The mass remains about 15.31 kg everywhere.
- Only the weight changes with g.
Q9. A friend says, “I am lighter on the Moon, so I can push the same heavy box more easily.” Do you agree? Justify using concepts of weight, mass, friction, and inertia.
Answer:
- On the Moon, your weight is less.
- But your mass and the box’s mass are the same.
- Inertia depends on mass, so the box still resists motion the same way.
- However, friction depends on normal force, which depends on weight.
- With lower weight, friction can be less, so sliding may be easier.
- So starting motion is still hard due to inertia, but reduced friction helps in sliding.
Q10. Your bathroom scale shows “60 kg” on Earth. Explain what this reading means. Convert it to newtons. Then predict the scale reading and true weight on the Moon.
Answer:
- Many bathroom scales show kg but actually sense force.
- On Earth, “60 kg” means a force equal to the weight of a 60 kg mass.
- True weight in newtons: W = m × g = 60 × 9.8 = 588 N.
- On the Moon, true weight is W ≈ 60 × 1.63 = 97.8 N.
- A scale calibrated for Earth g would not show “60 kg” on the Moon.
- It would show a much lower value because g is smaller there.