GRADE 9
2005
COMMON TASK FOR ASSESSMENT (CTA)
TECHNOLOGY
TEACHER'S BOOK
MEMORANDUM
SECTION B
Time : 2 hours
Marks : 80
TECHNOLOGY CTA 2005
1.
TEACHER'S BOOK – MEMORANDUM: SECTION B
Mechanisms are concerned with movement (motion). Name the four main
types of movement.
Linear
Rotary
Oscillating
Reciprocal
2.
Name the types of movement used in the following examples:
(a)
(b)
(c)
(d)
3.
4.
(1)
(1)
(1)
(1)
[4]
roatary
linear
oscillating
reciprocating
(1)
(1)
(1)
(1)
[4]
Levers can be divided into three classes. Name the class of lever for each
of the following sketches.
(a)
(b)
(c)
3rd class; effort is in the middle.
1st class; fulcrum is in the middle.
2nd class; load is in the middle.
(a)
Two of the examples shown in the figure below are paired first class
levers. Which objects are these?
A
C
(b)
(1 mark each x 2)
Which class of lever is each of the other two examples?
B
D
(c)
scissors
pliers
(2)
(2)
(2)
[6]
tweezers – 3rd class
nutcrackers – 2nd class
(1 mark each x 2)
Does a pair of tweezers offer any mechanical advantage? Explain
your answer.
No, it does not. There is no mechanical advantage with a third
class lever because the effort moves over a smaller distance
than the load. This is because the effort is closer to the fulcrum
than the load is to the fulcrum.
(d)
(3)
How do tweezers help us?
A third class lever is used to magnify movement.
(1)
[8]
1
TECHNOLOGY CTA 2005
5.
TEACHER'S BOOK – MEMORANDUM: SECTION B
Copy the following diagrams of linkages. Fill in the correct positions for the
fixed and moving pivots to give the required output movement. Use the key
below. Label the diagrams: FP for fixed pivot, MP for moving pivot.
Symbol
Type of Pivot
Fixed pivot (FP)
Moving pivot (MP)
(a)
(2)
(b)
(3)
[5]
6.
(a)
Identify the type of gear used in the picture below.
Bevel gear
(b)
What is the purpose of this type of gearing system?
Bevel gears change the axis of rotation.
7.
(a)
(b)
(c)
(1)
Calculate the input force required to move the boulder in picture A.
20 N x 3 m
60 N
Input force =
=
= 12 N
5m
5
Calculate the input force required to move the boulder in picture B.
20 N x 2 m
40 N
Input force =
=
= 8N
5m
5
Work out the mechanical advantage for picture A.
20 N
MA(A) =
= 1,67
12 N
(1)
[2]
(3)
(3)
(2)
2
(d)
(e)
Work out the mechanical advantage for picture B.
20 N
MA(B) =
= 2,5
8N
Which of these levers will give the better mechanical advantage –
picture A or picture B? Give reasons for your answer.
Picture B. The mechanical advantage is better as the load is
closer to the fulcrum.
8.
(2)
[12]
In a simple gear train the input gear (E) has 45 teeth and the output gear (F)
has 15 teeth.
(a)
If the required speed of the output shaft (axle) is 150 r.p.m.
(revolutions per minute), at what speed would the input shaft (axle)
have to turn? Show all your calculations.
Gear ratio =
gear E
= 45 = 3
gear F
15
The output gear turns 3 times as fast as the input gear.
Therefore Input speed = 150 r.p.m. ÷ 3 = 50 r.p.m.
(b)
(c)
(1)
What effect does this have on the output gear?
The output gear turns faster but with less force.
(a)
(4)
Is this gear system gearing up or gearing down?
Gearing up.
9.
(2)
In a simple gear train the input gear (X) has 10 teeth and turns at a
speed of 60 r.p.m. If the output gear (Y) has 30 teeth, what will the
speed (r.p.m.) be of the output shaft (axle)? Show all your
calculations.
gear X
= 10 = 1
Gear ratio =
gear Y
30
3
The output gear turns 1 the speed of the input gear.
3
Therefore Output speed = 60 r.p.m. x 1 = 20 r.p.m.
3
(2)
[7]
(1)
(1)
(2)
3
TECHNOLOGY CTA 2005
(b)
TEACHER'S BOOK – MEMORANDUM: SECTION B
In a compound gear train, the input gear (A) has 10 teeth and it turns
at 400 r.p.m. This is meshed with a second gear (B) which has 20
teeth on the same shaft (axle) as a third gear (C) with 10 teeth. If the
output speed is 100 r.p.m., what size (number of teeth) would the
output gear (D) need to be? Show all your calculations.
gear A
= 10 = 1
gear B
20
2
Output gear (B) turns 1 the speed of input gear (A).
2
Output speed (gear B) = 400 r.p.m. x 1 = 200 r.p.m.
2
Gear ratio =
(1)
(1)
(2)
This becomes input speed (gear C) = 200 r.p.m.
Required output speed (gear D) = 100 r.p.m.
The required output speed (gear D) is ½ as fast as the input
speed (gear C). Therefore if gear C has 10 teeth, then gear D
needs to have 20 teeth.
10.
(2)
(2)
[12]
You have been asked to generate an idea for a greeting card. The card
must use a system of levers.
(a)
Develop a design brief for this task.
Possible answer: Design and make a greeting card that uses a
system of levers.
(b)
List two constraints for the design.
–
–
(c)
(3)
must be a greeting card
must use a system of levers
Draw detailed sketches of your idea. Clarify your sketches with
necessary notes and labels. You must include the lever mechanism
in your sketches. Use arrows to show the direction of movement.
(1)
(1)
(8)
4
d
DESCRIPTORS
4
3
2
1
(d)
•
Develops an appropriate idea by drawing neat, accurate and detailed
freehand sketches.
•
The idea must be of a greeting card.
•
A good understanding of levers is demonstrated.
•
Comprehensive labels and notes explaining the sketches are given.
•
Develops an appropriate idea by drawing freehand sketches.
•
The idea must be of a greeting card.
•
A good understanding of levers is demonstrated.
•
Labels and notes explaining the sketch are included.
•
Develops an idea by drawing poor sketches.
•
The idea must be of a greeting card.
•
A poor understanding of levers is demonstrated.
•
Basic labels and notes are included.
•
Develops an inappropriate idea by drawing poor sketches which demonstrate
no understanding of levers.
MARKS
Fill in the correct positions for the fixed and moving pivots to give the
required output movement. Use the key below. Label the pivots: FP
for fixed pivot, MP for moving pivot.
Symbol
6–8
4–5
3
1–2
(4)
Type of Pivot
Fixed pivot (FP)
Moving pivot (MP)
5
TECHNOLOGY CTA 2005
LEVEL
4
TEACHER'S BOOK – MEMORANDUM: SECTION B
DESCRIPTORS
MARKS
Demonstrates an excellent understanding of levers and pivots by:
3
–
positioning all pivots correctly to give the required output movement
–
identifying all pivots using the correct symbol and label (FP or MP)
Demonstrates a good understanding of levers and pivots by:
2
–
positioning most pivots correctly to give the required output movement
–
identifying most pivots using the correct symbol and label (FP or MP)
Demonstrates a poor understanding of levers and pivots by:
1
–
positioning less than half the pivots correctly
–
identifying less than half the pivots
Demonstrates little understanding of levers and pivots by:
(e)
–
positioning less than a quarter of the pivots correctly
–
identifying less than a quarter of the pivots
Make a list of the materials that would be needed to make your
greeting card.
4
3
2
1
(3)
[20]
This list will vary according to the learner’s design. The teacher
must refer to the sketch to ensure that the list is relevant, and
assess accordingly.
6