Question

Answer the question
1.How can two machines appear identical and yet not have the same actual mechanical advantage?

2.What information would you use to calculate the efficiency of a machine?

3. When is the ideal mechanical advantage of a machine greater than 1?

4. Suppose you are an inventor in 1900. You are constructing a bicycle of you own design. What could you do to ensure your bicycle efficiently changes the work input into forward motion?

5. You have just designed a machine that uses 1000 J of work from a motor for every 800 J of useful work the machine supplies. What is the efficiency of your machine?

6. If a machine has an efficiency of 40% and you do 1000 J of work on the machine. what will be the work output of the machine?

Answer 1

1. Two machines can look identical but have different actual mechanical advantages because AMA depends on real operating conditions (friction, wear, misalignment, elasticity of parts, poor lubrication, manufacturing tolerances). These losses reduce the output force for a given input force, so otherwise identical-looking machines can give different AMA = Fout / Fin.

2. To calculate efficiency you need the useful output work (or power) and the input work (or power). Efficiency = (useful output work ÷ input work) × 100%. You can also compute it from input/output forces and distances or input/output powers if work values are not given.

3. The ideal mechanical advantage (IMA = input distance ÷ output distance) is greater than 1 when the input moves through a larger distance than the load (i.e., the machine is designed to multiply force). Examples: a long lever with a short resistance arm, multi‑pulley (block and tackle) systems, or a wheel-and-axle with a large wheel and small axle.

4. Ways (circa 1900) to make a bicycle efficiently convert input work to forward motion:
- Minimize drivetrain losses: use a well‑aligned chain drive, accurately cut sprockets, and tight chain engagement.
- Reduce bearing friction: use good lubrication and high‑quality (or ball) bearings in hubs, pedals and headset.
- Reduce rolling resistance: use properly inflated pneumatic tires and smooth tire treads.
- Reduce aerodynamic drag: streamline frame/profile and minimize frontal area and loose clothing.
- Reduce weight where practical and ensure frame stiffness to avoid energy loss by flexing.
- Maintain the machine: regular lubrication and adjustment to avoid extra friction.

5. Efficiency = 800 J ÷ 1000 J = 0.8 = 80%.

6. Output work = efficiency × input work = 0.40 × 1000 J = 400 J.