State what is meant by the mass of an object.
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Mass is a measure of the quantity of matter in an object at rest relative to the observer.
Mass And Weight
A student carries a 5 kg bag from the ground floor to the top floor of a building. Explain whether the mass of the bag changes during this journey.
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The mass does not change; because no matter has been added to or removed from the bag; mass is a property of the object and is independent of its position.
State two differences between mass and weight.
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Mass is measured in kg; weight is measured in N. Mass is a scalar quantity; weight is a vector quantity. Mass does not change with location; weight changes with gravitational field strength. (Any two pairs.)
An astronaut has a mass of 80 kg. Explain why the astronaut's weight on Mars is less than on Earth.
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Weight is the effect of a gravitational field on a mass; Mars has a weaker gravitational field than Earth / the gravitational field strength on Mars is smaller than on Earth; therefore the gravitational force acting on the astronaut's 80 kg mass is smaller on Mars; so the astronaut's weight decreases.
Calculate the weight of a 250 g apple on Earth where g = 9.8 N kg⁻¹.
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Finding the weight Equation used $$W=m\times g$$ Given $$m=250\text{ g}$$ $$g=9.8{\text{ N kg}}^{-1}$$ Converting mass to SI units $$m=\frac{250}{1000}$$ $$m=0.250\text{ kg}$$ Substitution $$W=0.250\times 9.8$$ $$W=2.45\text{ N}$$
An object has a weight of 36 N on Earth (g = 9.8 N kg⁻¹) and a weight of 6.0 N on the Moon. Calculate the gravitational field strength on the Moon and explain why the weight differs between the two locations.
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Finding the mass on Earth $$m=\frac{W}{g}$$ $$m=\frac{36}{9.8}$$ $$m=3.673...\text{ kg}$$ Finding the gravitational field strength on the Moon $${g}_{\text{Moon}}=\frac{W}{m}$$ $${g}_{\text{Moon}}=\frac{6.0}{3.673}$$ $${g}_{\text{Moon}}=1.63...\approx 1.6{\text{ N kg}}^{-1}\text{ (2 s.f.)}$$ The mass of the object is the same on both the Earth and the Moon; however, the Moon has a smaller gravitational field strength than the Earth; therefore the gravitational force acting on the same mass is smaller; so the weight on the Moon is less than the weight on Earth.
State how a beam balance is used to compare the masses of two objects.
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The unknown mass is placed on one pan and known standard masses are placed on the other pan; masses are added or removed until the beam is level / balanced; when balanced, the unknown mass equals the total known mass on the other side.
Explain why a beam balance gives the same result on the Moon as on Earth, but a spring balance does not.
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A beam balance compares masses by balancing the weight on each side; because both pans experience the same gravitational field strength, a change in g affects both sides equally; so the balance point does not change. A spring balance measures weight directly by the extension of a spring; on the Moon, g is smaller; therefore the weight is smaller; so the spring extends less and gives a lower reading.