In the velocity example, what drivetrain efficiency was assumed?

• A. 60 percent
• B. 75 percent
• C. 85 percent
• D. 90 percent

Answer: (B)

Drivetrain efficiency tells you what fraction of the motor’s output power actually reaches the wheels, after losses in gears, bearings, belts, and other transmission components. In the velocity example, a mid-range, practical value of 75 percent is used. This choice reflects a realistic balance: not all the motor power is lost to friction, but you don’t assume ideal, 100% transmission either. Using 75% means the power that drives the wheels is P_wheels = P_motor × 0.75, which leads to the velocity result shown in the example. If you used a higher efficiency, you’d predict a faster velocity; a lower efficiency would yield a slower one. The 75% assumption matches the scenario given and keeps the calculation straightforward.