Mass and weight — questions

1. state

Match each word to what it means, and each quantity to its unit.

Write the number of the matching option.

1. the amount of matter in the object
2. the gravitational force on the object
3. kilogram (kg)
4. newton (N)
5. metre (m)

• Mass: ______
• Weight: ______
• Unit of mass: ______
• Unit of weight: ______

Nudge (only if you are stuck): One of them is an amount of matter; the other is a pull. Which is measured on a spring balance?

2. calculate

A bag of potatoes has a mass of 2.4 kg. Calculate its weight on Earth, where g = 9.8 N/kg. Give your answer to 2 significant figures.

Weight of the bag on Earth: ______________ unit ________

Nudge (only if you are stuck): Weight = mass × gravitational field strength. Which unit does a weight have?

3. state / explain

A bag of sugar exactly balances a 1 kg mass on an equal-arm balance on Earth. An astronaut takes the balance, the sugar and the 1 kg mass to the Moon. What does the balance do there?

Circle one answer.

• It still balances
• The sugar side goes up
• The sugar side goes down
• It cannot be used on the Moon

Why?

Nudge (only if you are stuck): Both pans are on the Moon. Does the weaker pull act on one pan or on both?

4. complete

Complete the sentences. Around the Earth there is a gravitational ____ (1): a region where any mass feels a force. The force on a mass in it is the mass’s ____ (2). The force on each kilogram is the gravitational ____ ____ (3). On the Moon the field is weaker, so the same mass has a smaller ____ (4).

Gap 1

Gap 2

Gap 3

Gap 4

Nudge (only if you are stuck): The words you need are field, weight and field strength.

5. calculate / explain

An astronaut and her spacesuit have a mass of 75 kg on Earth. On the Moon the gravitational field strength is 1.6 N/kg. Find (a) the mass of the astronaut and suit on the Moon and (b) their weight on the Moon. Then explain why one of the two values changed and the other did not.

(a) Mass on the Moon: ______________ unit ________

(b) Weight on the Moon: ______________ unit ________

Why did one value change and the other not?

Nudge (only if you are stuck): Does anything leave the astronaut on the way to the Moon? Then use W = m × g.

6. state / explain

A stone is dropped near the Earth’s surface. Ignore air resistance. How does its speed change while it falls?

Circle one answer.

• It falls at a steady 9.8 m/s
• Its speed increases by 9.8 m/s every second
• Its speed increases by 9.8 N every second
• It depends on the mass of the stone

How is this linked to g = 9.8 N/kg?

Nudge (only if you are stuck): g = 9.8 N/kg is also the acceleration of free fall. What does an acceleration of 9.8 m/s² mean for the speed?

7. calculate

A rock of mass 5.0 kg has a weight of 18.5 N on Mars. Calculate the gravitational field strength on Mars. Give your answer to 2 significant figures, with its unit.

Gravitational field strength on Mars: ______________ unit ________

Nudge (only if you are stuck): Gravitational field strength is the force on each kilogram.

8. state / explain

Two parcels are put on the two pans of an equal-arm balance. The pan with parcel X goes down and the pan with parcel Y goes up. Which statement is correct?

Circle one answer.

• Y has the bigger mass
• X has the bigger weight, but the masses could be equal
• X has the bigger weight and the bigger mass
• X takes up more space than Y

Explain your choice.

Nudge (only if you are stuck): The pan that goes down is pulled harder. What does a bigger pull in the same field mean about the mass?

9. calculate / explain

A space probe has a mass of 800 kg. Near the cloud tops of Jupiter the gravitational force on it would be 19 800 N. (a) What is the probe’s mass near Jupiter? (b) Calculate the gravitational field strength there, to 2 significant figures. Then say what your answer to (b) means for each kilogram of the probe. (c) A small part breaks off and falls freely near the cloud tops (ignore the gas around it). What is its acceleration?

(a) Mass near Jupiter: ______________ unit ________

(b) Gravitational field strength near Jupiter: ______________ unit ________

(c) Acceleration of the falling part: ______________ unit ________

What does your value of g mean for each kilogram of the probe?

Nudge (only if you are stuck): Mass first: has the probe changed? Then share the force between the kilograms. For (c), what else does g tell you?

10. predict / explain

A shop on a future Mars base has two ways to weigh out rice: an old equal-arm balance with a set of standard masses from Earth, and a spring balance whose scale was marked in kilograms on Earth. (a) Will the equal-arm balance give customers the right mass of rice? (b) Will the spring balance? Explain both answers.

(a) Equal-arm balance, and why

(b) Spring balance, and why

Nudge (only if you are stuck): Which of the two compares the rice with known masses, and which measures the pull on the rice?