Question

The kinetic energy of a body is 'K. If one-fourth of its mass is removed and velocity is doubled, its new kinetic energy is,

• A. $K$
• B. $3K$
• C. $4K$
• D. $\frac{9K}{4}$

Answer 1

The correct option is B $3K$

We have $K.E=\frac{1}{2}m{v}^2$

where $m$ is the mass and $v$ is the velocity.

Now,

New mass $=m-\frac{m}{4}=\frac{3}{4}m$

New velocity $=2v$

Now $K.E=K=\frac{1}{2}\times \frac{3}{4}m\times (2v{)}^2=\frac{3m{v}^2}{2}=3K$