You could instead get a random angle (within some range) and then use that for the initial direction of the ball. Something like:

// min angle: 10, max angle: 170
int min_angle = 10;
int max_angle = 170;
int degrees = arc4random_uniform(max_angle) + min_angle;
float radians = degrees * M_PI/180.0f;
myVector = CGVectorMake(cos(radians), sin(radians));

This will be a unit direction vector though, so, you would want to multiply this by whatever amount of force you want in this direction.

You could instead get a random angle (within some range) and then use that for the initial direction of the ball. Something like:

// min angle: 10, max angle: 170
int min_angle = 10;
int max_angle = 170;
int degrees = arc4random_uniform(max_angle - min_angle) + min_angle;
float radians = degrees * M_PI/180.0f;
myVector = CGVectorMake(cos(radians), sin(radians));

This will be a unit direction vector though, so, you would want to multiply this by whatever amount of force you want in this direction.