The kinetic energy of a body of mass $m$ moving with speed $v$ is:
A$mv$
B$\dfrac{1}{2} m v^2$
C$m v^2$
D$\dfrac{1}{2} m v$
Answer & Solution
Correct answer: B. $\dfrac{1}{2} m v^2$
Kinetic energy: $KE = \tfrac{1}{2} m v^2$. Notice the factor of $\tfrac{1}{2}$ and the $v^2$ dependence.
The quadratic dependence is why a car at 60 km/h has four times the kinetic energy of the same car at 30 km/h, not twice. Stopping distance also scales as $v^2$ for the same brakes.
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