alleryStart learning →A train accelerates from rest to 30.0 km/h in 20.0 s. What is its average acceleration in SI units?
A1.50 m/s^2
B0.833 m/s^2
C0.417 m/s^2
D4.17 m/s^2
Answer & Solution
Correct answer: C. 0.417 m/s^2
1. The train starts from rest, so the change in velocity is +30.0 km/h.
2. The units are mixed, so convert the velocity to metres per second first.
3. Substitute the conversion factors: 30.0 km/h x (1000 m / 1 km) x (1 h / 3600 s) = 8.33 m/s.
4. Average acceleration is the change in velocity divided by the elapsed time.
5. Substitute the values: (8.33 m/s) / (20.0 s) = 0.417 m/s^2.
6. Dividing 30.0 by 20.0 without converting gives 1.50, which carries the wrong units.
_Source: OpenStax College Physics (CC BY 4.0), Ch 2 "Kinematics", section 2.4 Acceleration_
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