alleryStart learning →A rocket starts from rest and accelerates at 20 m/s^2. How long does it take to reach a velocity of 400 m/s?
A8000 s
B40 s
C10 s
D20 s
Answer & Solution
Correct answer: D. 20 s
1. Identify the knowns: the initial velocity is 0, the final velocity is 400 m/s and the acceleration is 20 m/s^2.
2. Choose the equation linking velocity, acceleration and time.
3. Rearranged, the time equals the change in velocity divided by the acceleration.
4. Substitute the values: (400 m/s - 0 m/s) / (20 m/s^2) = 20 s.
5. Multiplying the two given values gives 8000, which is not a time at all.
_Source: OpenStax College Physics (CC BY 4.0), Ch 2 "Kinematics", section 2.5 Motion Equations for Constant Acceleration in One Dimension_
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