ASVAB (Armed Services Vocational Aptitude Battery)Mechanical Comprehension (MC)Easy
A technician is evaluating the efficiency of a simple pulley system used to lift a 100 kg load. The technician observes that 1200 Joules of work are put into the system, but only 900 Joules of work are done on the load. What is the efficiency of this pulley system?
- A90%
- B80%
- C65%
- D75%
Show answer & explanationAnswer & explanation
Correct answer: D. 75%
Efficiency is calculated as the ratio of useful work output to the total work input, multiplied by 100%. In this case, (900 J / 1200 J) * 100% equals 75%.
Why the other options are wrong
- A. Incorrect calculation. The efficiency is significantly lower than 90%.
- B. Incorrect calculation. The ratio is 0.75, not 0.80.
- C. Incorrect calculation. 900/1200 = 0.75, not 0.65.
Mechanical Efficiency
The ratio of useful work output to the total work input, expressed as a percentage. It indicates how effectively a machine converts input energy into useful output energy.
- Always less than 100% due to friction and other energy losses.
- Calculated as (Work Output / Work Input) * 100%.
- A measure of energy conservation in a system.
Memory trick: Efficient machines produce 'output' from 'input' with minimal 'loss'.