This question involves the concepts of centripetal acceleration and radius of the circlular path.
The acceleration of the ball will change by a factor of "0.5".
The centripetal acceleration of the ball is given by the following formula:
[tex]a_c=\frac{v^2}{r}-------------- eqn(1)[/tex]
where,
v = speed
r = distance of mass from center = radius of circular path = 4 m/s²
[tex]a_c[/tex] = centripetal acceleration
Therefore, when the radius of the circular path is doubled, the centripetal acceleration becomes:
[tex]a_c'=\frac{v^2}{2r}\\\\a_c'=0.5\frac{v^2}{r}\\\\using\ eqn\ (1):\\\\a_c'=0.5\ a_c[/tex]
Learn more about the centripetal acceleration here:
brainly.com/question/14465119?referrer=searchResults
The attached picture explains the concept of centripetal acceleration.