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WAEC Physics 2018 Paper

Question : 34

Total: 50

When the speed of a car is halved, its kinetic energy is

Solution:

Concept:

Kinetic energy depends on the square of speed.

Explanation:

Let the original kinetic energy be

K = \frac{1}{2}mv^{2}

When the speed is halved, the new speed is

\frac{v}{2}

New kinetic energy:

K' = \frac{1}{2}m\left(\frac{v}{2}\right)^{2}

K' = \frac{1}{2}m \cdot \frac{v^{2}}{4}

K' = \frac{1}{4}\left(\frac{1}{2}mv^{2}\right) = \frac{K}{4}

So the kinetic energy becomes one quarter of its original value.

Answer:

The kinetic energy is quartered. Correct option: B.

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