Physics · Professor Newton

Every card in Forces and motion, Year 7: more practice

The whole deck, in order — so you can read it through before your child ever sees it.

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1 KS3-PHYS-FOR-0049

A car travels at a steady 72 km/h. What is its speed in m/s? (number only)

20

HintChange kilometres to metres and hours to seconds.

Why72 km/h = 72 000 m per 3600 s = 20 m/s. A shortcut is to divide by 3.6.

2 KS3-PHYS-FOR-0050

What can an unbalanced force do to a moving object?

Change its speed or direction

HintThink of what a resultant force does to motion.

WhyAn unbalanced force changes the motion of the object: it speeds it up, slows it down or turns it.

3 KS3-PHYS-FOR-0051

Which non-contact force acts between two magnets?

Magnetic force

HintIt can push or pull across a gap, like gravity does.

WhyMagnets push or pull each other across a gap without touching, just as gravity does.

4 KS3-PHYS-FOR-0052

Is air resistance a contact force or a non-contact force?

A contact force

HintThink about what is touching the object.

WhyAir resistance is caused by the air particles hitting the surface of the moving object.

5 KS3-PHYS-FOR-0053

A newtonmeter reads 0.2 N with nothing hanging on it. What is the name of this fault?

A zero error

HintThe scale does not start where it should.

WhyBefore using the instrument, adjust the reading to 0 or subtract the error from every result.

6 KS3-PHYS-FOR-0054

Roughly what is the weight of a 1 kg bag of sugar on Earth, in newtons? (number only)

10

HintOn Earth, 1 kg is pulled by about 10 N.

WhyGravity pulls each kilogram with a force of about 10 N, so 1 kg weighs about 10 N (more exactly 9.8 N).

7 KS3-PHYS-FOR-0055

On a force diagram 1 cm stands for 2 N. How long, in cm, is the arrow for a 10 N force? (number only)

5

HintDivide the force by the size of one centimetre.

Why10 ÷ 2 = 5 cm.

8 KS3-PHYS-FOR-0056

Why is oil put on a bicycle chain?

To reduce friction

HintThink of the surfaces rubbing together.

WhyA lubricant forms a thin layer between the parts so they slide past each other more easily and wear less.

9 KS3-PHYS-FOR-0057

A spring has a natural length of 12 cm. Under a load it is 19 cm long. What is its extension in cm? (number only)

7

HintExtension is the increase in length.

WhyExtension = stretched length − natural length = 19 − 12 = 7 cm.

10 KS3-PHYS-FOR-0058

What happens to a spring that is stretched beyond its elastic limit?

It does not go back to its original length

HintThink about the meaning of 'elastic'.

WhyPast the limit the spring is permanently stretched. Below it, the spring returns to its original length when the load is removed.

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