Answer:
All of them: change velocity, accelerate, change position
Explanation:
We can answer this question by using Newton's second law:
F = ma
where
F is the net force on the object
m is the mass of the object
a is the acceleration
We notice that when there is an unbalanced force on the object,
, and therefore

whcih means that the object will accelerate.
But acceleration is the rate of change of velocity, v:

And so,

which means that the object will change velocity.
If the object is changing velocity, this means that it is also moving: therefore, the position of the object must be changing, so also the option "change position" is correct.
Explanation:
Length of a string, l = 0.626 m
A tennis ball revolves in a horizontal circle above his head at a rate of 4.50 rev/s.
(a) The centripetal acceleration of the tennis ball is given by :

(b) When r = 0.626 m and ω = 4.50 rev/s
Speed,

When r = 1 m and ω = 4 rev/s
Speed,

Speed is more in second case when child now increases the length of the string to 1.00m but has to decrease the rate of rotation to 4.00 rev/s.
(c) 
Hence, this is the required solution.