The momentum of a body is increased by 50%. The percentage increase in the kinetic energy of the body is ______%.

We need to find the percentage increase in kinetic energy when momentum is increased by 50%.

Relationship between kinetic energy and momentum: $$KE = \frac{p^2}{2m}$$

New momentum. If momentum increases by 50%: $$p' = 1.5p = \frac{3p}{2}$$

New kinetic energy: $$KE' = \frac{(p')^2}{2m} = \frac{(1.5p)^2}{2m} = \frac{2.25p^2}{2m} = 2.25 \times KE$$

Percentage increase: $$\% \text{ increase} = \frac{KE' - KE}{KE} \times 100 = (2.25 - 1) \times 100 = 125\%$$

The correct answer is 125%.