The same car travelling at 30.0 m/s brakes on wet concrete, where the deceleration is only 5.00 m/s^2. What distance does it cover while braking?
A45.0 m
B64.3 m
C180 m
D90.0 m
Answer & Solution
Correct answer: D. 90.0 m
1. Identify the knowns: the initial velocity is 30.0 m/s, the final velocity is 0 and the acceleration is -5.00 m/s^2.
2. Use the same relation as for dry concrete, with the smaller deceleration substituted.
3. The displacement equals the difference of the squared velocities divided by twice the acceleration.
4. Substitute the values: (0 - 900 m^2/s^2) / (2 x (-5.00 m/s^2)) = 90.0 m.
5. Wet concrete needs a longer stopping distance than the 64.3 m of dry concrete, as expected.
_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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