ASVAB (Armed Services Vocational Aptitude Battery)Mechanical Comprehension (MC)Medium
A technician is evaluating the power output of a motor. The motor lifts a 50 kg mass vertically by 10 meters in 5 seconds. What is the power output of the motor?
- A100 Watts
- B200 Watts
- C500 Watts
- D1000 Watts
Show answer & explanationAnswer & explanation
Correct answer: D. 1000 Watts
Power is the rate at which work is done (Power = Work / Time). Work done against gravity is Work = Force × Distance = (mass × gravity) × distance. So, Work = (50 kg × 9.8 m/s²) × 10 m = 4900 Joules. Power = 4900 J / 5 s = 980 Watts. Rounding to the nearest significant figure, or using g=10 m/s² for simplicity often used in such problems, Work = (50 kg × 10 m/s²) × 10 m = 5000 J. Power = 5000 J / 5 s = 1000 Watts.
Why the other options are wrong
- A. This is incorrect; it's a significant underestimation of the power.
- B. This is incorrect; it does not accurately represent the work done over time.
- C. This is incorrect; it's a miscalculation of either work or time.
Mechanical Power
Mechanical power is the rate at which work is performed or energy is transferred. It is calculated as work divided by time (P = W/t) or force multiplied by velocity (P = Fv).
- Unit is Watts (Joules per second).
- Work done against gravity is Force × Distance (mgh).
- Higher power means work is done faster.
Memory trick: Power is 'Work' done over 'Time', or 'Force' times 'Velocity'.