When the velocity of a body is doubled, the momentum of the body:

Concept: Momentum (P): The product of mass and velocity is called momentum. 

Momentum $\left(\mathrm{P}\right)=mass\left(\mathrm{m}\right)\times \text{ Velocity }\left(\mathrm{v}\right)$
We know that velocity is directly proportional to momentum

$P_1=m\times V$

According to the question, If velocity is double then
$P_2=m\times 2V$
$\frac{P_1}{P_2}= \frac{m\times v}{m\times 2v}$

$P_2= 2P_1$
Hence, if velocity is doubled then momentum also gets doubled.