Example 1 · level 1
Find the weight (in N) of a 6 kg sack of rice on Earth. Take g = 9.8 m/s².
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- W = 6 × 9.8 = 58.8 N.
Answer: 58.8 N
CLASS 9 SCIENCE · GRAVITATION
Mass and weight (Earth, Moon, planets)
Weight W = mg. Mass stays the same everywhere; weight changes with g. On the Moon g is about 1/6 of g on Earth.
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Worked examples
Example 2 · level 2
An astronaut of mass 42 kg goes to the Moon, where g is 1/6 of Earth's. Find the astronaut's weight on the Moon (in N). Take g on Earth = 9.8 m/s².
Show solution
- W(Earth) = 411.6 N.
- W(Moon) = 411.6 ÷ 6 = 68.6 N.
Answer: 68.6 N
Example 3 · level 3
A rover weighs 529.2 N on Earth (g = 9.8 m/s²). What would it weigh on Mercury, where g = 3.7 m/s²? (in N, correct to 2 decimal places)
Show solution
- m = 529.2 ÷ 9.8 = 54 kg.
- W(Mercury) = 54 × 3.7 = 199.8 N.
Answer: 199.8 N