ASVAB (Armed Services Vocational Aptitude Battery)Mechanical Comprehension (MC)Medium
A worker is using a simple machine to lift a heavy box. If the worker applies a force of 100 N over a distance of 2 meters, and the machine lifts the box, which weighs 300 N, a distance of 0.5 meters, what is the efficiency of the simple machine?
- A25%
- B150%
- C75%
- D200%
Show answer & explanationAnswer & explanation
Correct answer: C. 75%
Efficiency is calculated as the ratio of useful work output to total work input, multiplied by 100%. In this case, the work output is (300 N * 0.5 m) = 150 J, and the work input is (100 N * 2 m) = 200 J. Therefore, the efficiency is (150 J / 200 J) * 100% = 75%.
Why the other options are wrong
- A. This would be the result if the work input was 600 J, or if the work output was 50 J.
- B. This would imply the machine creates energy, which is impossible; it might result from an inverted calculation.
- D. This would imply the machine creates energy, which is impossible; it might result from an inverted calculation with incorrect values.
Mechanical Efficiency
The ratio of useful work output to the total work input, expressed as a percentage.
- Always less than 100% for real machines due to friction and other energy losses.
- Indicates how effectively a machine converts input energy into useful output energy.
- Calculated as (Work Output / Work Input) * 100%.
Memory trick: Efficiency EArns Output Over Input.