Mechanical Properties of Materials

14 Grade 10 Physics questions on Mechanical Properties of Materials, with worked marking schemes. 14 questions are available on this topic in full.

1. Question 1

   1 mark

   A fixed load is hung on a wire and the extension is measured. Which one of the following changes would reduce the extension produced by the same load?

   A. Increasing the cross-sectional area of the wire.

   B. Using a wire of a more ductile material.

   C. Reducing the diameter of the wire.

   D. Increasing the original length of the wire.

   (1 mark)

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2. Question 2

   1 mark

   A blacksmith compares two panga blades by trying to scratch the surface of each one with a steel file. The property of the blades being compared is:

   A. density.

   B. toughness.

   C. hardness.

   D. elasticity.

   (1 mark)

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3. Question 3

   4 marks

   The breaking stress of a certain steel is $4.0\times 10^8$ Pa.

   (a) Determine the maximum load that a rod of this steel of cross-sectional area $5.0\times 10^{-5}$ m² can support.

   (b) Give two reasons why, in practice, the rod would be used to carry a load much smaller than this value.

   (4 marks)

   Marking scheme

   (a) 1 mark: Maximum load = breaking stress x cross-sectional area = $4.0\times 10^8$ x $5.0\times 10^{-5}$. (a) 1 mark: = $2.0\times 10^4$ N (20 000 N). (b) 1 mark: The rod may contain hidden flaws, or may be weakened over time by rusting or by fatigue from repeated loading, so its real breaking load is lower than the calculated value. (b) 1 mark: A sudden (shock) load or an unexpected extra load raises the stress briefly far above the steady value, so a safety margin is left to prevent the rod snapping without warning.

4. Question 4

   3 marks

   A learner bends a piece of fencing wire to and fro repeatedly at the same point until it snaps, even though a single pull of the same size would not break it. Explain this observation.

   (3 marks)

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5. Question 5

   1 mark

   A material that can absorb a large amount of energy and deform a great deal before it finally fractures is best described as:

   A. brittle.

   B. dense.

   C. hard.

   D. tough.

   (1 mark)

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6. Question 6

   1 mark

   A copper wire of cross-sectional area $2.0\times 10^{-6}$ m² supports a load of 30 N. The tensile stress in the wire is:

   A. $6.0\times 10^{-5}$ Pa

   B. $1.5\times 10^7$ Pa

   C. $1.5\times 10^5$ Pa

   D. $6.7\times 10^{-8}$ Pa

   (1 mark)

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7. Question 7

   6 marks

   Describe an experiment you would carry out in the school laboratory to investigate how the extension of a spiral spring depends on the stretching force applied to it.

   (6 marks)

   Marking scheme

   1 mark: Apparatus - spiral spring, retort stand and clamp, pointer, metre rule (or half-metre rule), set of slotted masses. 1 mark: Suspend the spring vertically from the clamp and record the initial pointer reading on the metre rule with no load. 1 mark: Hang a known mass on the spring, record the new pointer reading, and obtain the extension as new reading minus initial reading. 1 mark: Repeat for at least six increasing masses, each time converting mass to stretching force using F = mg (g = 10 N/kg), taking care not to exceed the elastic limit. 1 mark: Tabulate force against extension and plot a graph of stretching force (y-axis) against extension (x-axis). 1 mark: A straight line passing through the origin shows that extension is directly proportional to the stretching force; the slope of the line gives the spring constant.

8. Question 8

   1 mark

   A steel wire supporting a hoist in a sisal factory is stretched beyond its elastic limit. When the load is completely removed, the wire will:

   A. become shorter than it was before the load was applied.

   B. remain permanently longer than it was before the load was applied.

   C. slowly return to its original length after a few hours.

   D. return at once to its original length.

   (1 mark)

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9. Question 9

   1 mark

   A steel rod of original length 2.0 m stretches by 4.0 mm when a load is hung on it. The tensile strain in the rod is:

   A. $8.0\times 10^{-3}$ m

   B. $5.0\times 10^2$, no units

   C. $2.0\times 10^{-3}$, no units

   D. $2.0\times 10^{-3}$ m

   (1 mark)

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10. Question 10

    4 marks

    Distinguish between a tensile force and a compressive force acting on a material, and give one example of a part of a building in which each type of force acts.

    (4 marks)

    Marking scheme

    1 mark: A tensile force is a stretching (pulling) force that tends to increase the length of a material. 1 mark: A compressive force is a squeezing (pushing) force that tends to reduce the length of a material. 1 mark: Example of tensile force - the steel rods in the lower part of a reinforced concrete beam / a wire supporting a hanging water tank (any correct example). 1 mark: Example of compressive force - a pillar or column carrying the weight of an upper floor / a foundation stone (any correct example).

11. Question 11

    4 marks

    Distinguish between a ductile material and a brittle material, and give one example of each.

    (4 marks)

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12. Question 12

    1 mark

    A learner hangs different loads on a spiral spring clamped to a retort stand and measures the extension each time. While the spring is still obeying Hooke's law, which statement about the spring is correct?

    A. The extension remains the same however much the stretching force is increased.

    B. The stretching force is directly proportional to the original length of the spring.

    C. The extension is directly proportional to the square of the stretching force.

    D. The extension is directly proportional to the stretching force.

    (1 mark)

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13. Question 13

    4 marks

    A spring balance used at a produce store extends by 2.5 cm when a load of 5.0 N is hung on it.

    (a) Determine the spring constant of the spring.

    (b) Determine the extension produced by a load of 12 N, assuming the elastic limit is not exceeded.

    (4 marks)

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14. Question 14

    4 marks

    The leaf springs fitted under the body of a matatu are made of specially treated steel. Suggest two properties the steel must have for this use, giving a reason for each.

    (4 marks)

    Marking scheme

    1 mark: It must have a high elastic limit / be highly elastic. 1 mark: Reason - it must return to its original shape after each bump so the springs are not permanently bent by heavy loads. 1 mark: It must be tough (not brittle) / resistant to fatigue. 1 mark: Reason - it is flexed thousands of times on rough roads and must absorb the energy without cracking or snapping. (Accept high tensile strength with the reason that it must carry heavy passenger loads without breaking.)

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