Kinetic Energy

Question

A 2 kg cricket ball is thrown so that it travels horizontally with a speed of 10 m/s just after release. What is the translational kinetic energy of the ball at that instant?

RankGuru · Accepted Answer

Kinetic energy is the energy a body possesses by virtue of its motion and is given by $K = 	frac{1}{2}mv^2$, where $m$ is the mass and $v$ the speed. It is a scalar quantity that scales linearly with mass but quadratically with speed, which is why doubling speed quadruples the energy. Substituting $m = 2	ext{ kg}$ and $v = 10	ext{ m/s}$ yields $K = 	frac{1}{2}(2)(10)^2 = 	frac{1}{2}(2)(100) = 100	ext{ J}$. The option 200 J forgets the factor of one-half. The option 20 J incorrectly uses $v$ linearly instead of $v^2$. The option 50 J halves the mass contribution without justification. This is the standard NCERT relation for the kinetic energy of a point mass. As a sanity check, the joule is equivalent to $	ext{kg}\,	ext{m}^2/	ext{s}^2$, and $2 	imes 10^2 / 2 = 100$ reproduces both the correct units and magnitude expected for an everyday thrown ball.

Kinetic Energy

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