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A cricket ball of mass $0.15$ kg moves at $20$ m/s. Its kinetic energy is:
A$15$ J, taking $K = \tfrac{1}{2}mv$ without squaring it
B$30$ J, since $K = \tfrac{1}{2}\cdot 0.15\cdot 400 = 30$
C$60$ J, equal to $mv^2$ without the half factor
D$3$ J, scaling only by mass and not by squared speed
Answer & Solution
Correct answer: B. $30$ J, since $K = \tfrac{1}{2}\cdot 0.15\cdot 400 = 30$
$K = \tfrac{1}{2}\cdot 0.15\cdot 20^2 = 30$ J.
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