Engineering · Mock exam 2026 All mock exam questions
Mock exam · Section 2 · Written response

Question 11

[4 marks] Simple familiar
The question

Explain how a screw jack provides a mechanical advantage when raising a car. Include a sketch to support your response.

[4 marks]

Watch the situation first

The handle travels a long way so the car can rise a little

Not to scale, and the pitch is drawn much larger than it really is. Watch how far the handle tip travels in one turn, and how little the car rises.

Turning the handle drives the screw up through the body of the jack One turn: the effort travels the whole dashed circle, a distance of 2πr In that same turn, the pad and the car rise only one pitch, P VR = 2πr ÷ P is large. Three turns lift the car only 3P MA = FL ÷ FE rises with VR, so a small effort lifts the car car FL load force of the car P FE 2πr r car has risen P car has risen 2P car has risen 3P Turns of handle 0 1 2 3 Effort moved 0 2πr 2 × 2πr 3 × 2πr Load risen 0 P 2P 3P

Every turn, the effort travels the full circle of the handle, 2πr, while the load rises one pitch, P. That large distance ratio is what lets a small effort force lift the car.

Now for the engineering

Change the handle and the pitch, and watch the VR

Set the handle radius and the pitch, then turn the handle. The readouts compare the distance the effort moves with the distance the load rises. The MA shown is the ideal MA, with no friction, which equals the VR.

load FL P 2πr pad start rise
Path of the handle tip, 2πr per turn Distance the effort has moved

The pitch is drawn 5 times larger than the handle, so you can see the threads.

In one turn
Velocity ratio
Ideal mechanical advantage (no friction)
So far

Marking guide · 4 marks

Work through the model response one mark at a time

Try to write each sentence yourself before you reveal it. Three marks are for the wording and one is for the sketch.

Mark 1The function of the jack

A screw jack converts the rotary motion of the handle into slow linear motion of the lifting pad, so a small effort force ($F_E$) at the handle produces a large load force ($F_L$) that lifts the car.

Why?

You name the small effort at the handle being converted into a large load force lifting the car.

Marking

For the function, accept wording that the screw converts rotary motion into linear motion to lift the load.

Marker: explains the function of a screw jack appropriately, including wording relating to a small effort force at the handle being converted into a large load force that lifts the car

Mark 2Velocity ratio

In one turn, the effort moves through the circumference of the handle's circle ($2\pi r$) while the load rises only one pitch ($P$), so VR = circumference/pitch is large.

Why?

You state, in words, that the effort travels $2\pi r$ while the load rises one pitch per turn, and you link this to VR.

Marking

Accept VR for screws = circumference/pitch, or $2\pi r/P$, when it is accompanied by wording. Equations without words relating the concepts do not earn the mark.

Marker: uses the concept of VR appropriately, including wording that indicates the effort moves through the circumference of the handle's circle while the load rises one pitch per turn

Mark 3Mechanical advantage

MA $= F_L/F_E$ rises with VR, so a longer handle or a finer pitch increases the VR and the MA, and less effort is needed to lift the car.

Why?

You link MA to VR and state that a longer handle or a finer pitch reduces the effort needed.

Marking

For MA, also accept the reverse: a shorter handle or a coarser pitch means more effort is needed.

Marker: uses the concept of MA appropriately, including wording that indicates that a longer handle (or a finer pitch) increases the VR and the MA, so the effort required to lift the load reduces

Mark 4The annotated sketch

Sketch: screw jack with base, threaded screw and lifting pad under the car. Handle of radius $r$ with its circular path dashed. Arrows labelled effort force $F_E$ at the handle tip and load force $F_L$ on the pad. Pitch $P$ between adjacent threads.

load force FL (car) effort force FE handle radius r pitch P effort moves 2πr per turn of handle load rises one pitch per turn
Why?

Your sketch labels $F_E$, $F_L$, $r$ and $P$ on a recognisable screw jack.

Marking

An appropriate sketch includes effort force ($F_E$) and load force ($F_L$) and/or handle radius ($r$) and pitch ($P$). Students may use any object to represent the load.

Or other suitable response consistent with a reasonable understanding.

Marker: includes an appropriate annotated sketch of a screw jack

The model response in full

A screw jack converts the rotary motion of the handle into slow linear motion of the lifting pad, so a small effort force ($F_E$) at the handle produces a large load force ($F_L$) that lifts the car. Mark 1

In one turn, the effort moves through the circumference of the handle's circle ($2\pi r$) while the load rises only one pitch ($P$), so VR = circumference/pitch is large. Mark 2

MA $= F_L/F_E$ rises with VR, so a longer handle or a finer pitch increases the VR and the MA, and less effort is needed to lift the car. Mark 3

Sketch: screw jack with base, threaded screw and lifting pad under the car. Handle of radius $r$ with its circular path dashed. Arrows labelled effort force $F_E$ at the handle tip and load force $F_L$ on the pad. Pitch $P$ between adjacent threads. Mark 4

Putting it all together

Each phrase of the question gave you something

“Explain how a screw jack”
Say what it does. The rotary motion of the handle becomes slow linear motion of the pad, so a small effort force lifts a large load force.
“provides a mechanical advantage”
Two concepts, both in words. VR: the effort moves $2\pi r$ while the load rises one pitch $P$. MA $=F_L/F_E$ rises with VR, so a longer handle or a finer pitch means less effort.
“when raising a car”
The car is the load force $F_L$ on the pad. The effort force $F_E$ acts at the handle tip.
“Include a sketch to support your response”
A mark of its own. Label $F_E$, $F_L$, the handle radius $r$ with its dashed path, and the pitch $P$ between adjacent threads.
Common errors

If I had to guess where you might lose marks…

  • The equation on its own. Writing VR = circumference/pitch with no words explaining what moves where earns nothing. Say that the effort moves $2\pi r$ while the load rises one pitch.
  • Energy from nowhere. Saying the screw jack creates or multiplies energy or work is wrong. It trades a large effort distance for a small load distance.
  • The relationship reversed. Claiming a coarser pitch or a shorter handle makes lifting easier. Both lower the VR and the MA, so more effort is needed.
  • A sketch that does not earn its mark. Drawing a jack with no labels, or labelling the pitch as the whole thread length instead of the distance between adjacent threads.
Compare with past QCAA questions

The past QCAA questions this one was modelled on

2024 Question 11
Short response · 4 marks
Explain what a crowbar is for using MA and VR, with a labelled sketch.
2022 Question 11
Short response · 5 marks
Explain MA and VR with a simple pulley system and an annotated sketch.

All past QCAA Engineering questions

Only mark this done when you could do it without help. Reading the solution does not count.

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A Tangent Tuition mock exam question. It is not a past QCAA question, and Tangent Tuition is not affiliated with the QCAA.

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