Question 1

What is the difference between a first-class and a second-class lever?

Accepted Answer

In a first-class lever, the fulcrum is between the effort and the load (e.g., a seesaw or crowbar). In a second-class lever, the load is between the fulcrum and the effort (e.g., a wheelbarrow or nutcracker). Second-class levers always have a mechanical advantage greater than 1, meaning they multiply force. First-class levers can have a mechanical advantage greater than, less than, or equal to 1 depending on the position of the fulcrum.

Question 2

How do I calculate gear ratios?

Accepted Answer

To calculate the gear ratio between two gears, divide the number of teeth on the driven gear (output) by the number of teeth on the driver gear (input). For example, if the driver has 20 teeth and the driven has 60 teeth, the ratio is 60/20 = 3:1. This means the driven gear rotates once for every three rotations of the driver, but it has three times the torque. If you need to find the output speed, multiply the input speed by the inverse of the ratio (e.g., input 100 rpm gives output 100/3 ≈ 33.3 rpm).

Question 3

What is the difference between thermoplastic and thermosetting polymers?

Accepted Answer

Thermoplastics (e.g., HDPE, acrylic) can be repeatedly softened by heating and hardened by cooling, making them recyclable. They have a linear or branched polymer structure. Thermosetting polymers (e.g., epoxy resin, melamine formaldehyde) undergo an irreversible chemical change when heated, forming cross-linked structures. Once set, they cannot be remelted, so they are not recyclable but are more heat-resistant and rigid. This affects their use: thermoplastics are used for packaging and bottles, while thermosets are used for electrical insulators and adhesives.

Question 4

How do I remember the different material properties?

Accepted Answer

Use mnemonics! For example, 'HET M' for Hardness, Elasticity, Toughness, Malleability. Or create a story: 'A hard, elastic band is tough and malleable.' Also, link each property to a real-world example: hardness = diamond drill bit, toughness = rubber mallet, elasticity = rubber band, malleability = gold leaf. Practice by describing a material (e.g., 'Mild steel is tough and ductile but not very hard').

Question 5

What is the life cycle assessment (LCA) and why is it important?

Accepted Answer

LCA is a method to evaluate the environmental impact of a product from raw material extraction to disposal (cradle to grave). It considers energy use, pollution, and waste at each stage. It's important because it helps designers make sustainable choices, like using recycled materials or designing for disassembly. In the exam, you might be asked to compare two products using LCA or suggest improvements to reduce environmental impact. Remember the six stages: extraction, manufacturing, packaging, use, disposal, and recycling.

Question 6

How do I calculate the mechanical advantage of a lever?

Accepted Answer

Mechanical advantage (MA) = load / effort. Alternatively, for a lever, MA = distance from effort to fulcrum / distance from load to fulcrum. For example, if the effort arm is 2 m and the load arm is 0.5 m, MA = 2 / 0.5 = 4. This means the lever multiplies the effort force by 4. If you apply 10 N of effort, you can lift a 40 N load. Remember that MA > 1 means force is multiplied, MA < 1 means speed/distance is multiplied.

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