Question

If an unbalanced force acts on an object, how does the speed of the object change with the size of the force? How does the speed change with the mass of the object?

Answer 1

When a body is under the action of several forces in that situation a lot of forces cancels out each other nor balances each other only a few remaining unbalanced forces motion in the body
-The momentum of a body is defined as the product of the mass of the body and its velocity it is generally defined as the motion content of the body

Complete step by step answer:
That the vector sum of all forces acting on a body is equal to 0 then the object would have zero acceleration, as per Newton's first law but If there is an "unbalanced force" acting on an object, this essentially means that the vector sum of all forces acting on does not equal 0
The acceleration of the object is given by Newton's second law which can be written as $\Sigma \vec F = m\vec a$
By rearranging this equation to solve for the acceleration we have:
$\vec a = \dfrac{{\Sigma \vec F}}{m}$ (1)
Now we want to calculate the velocity of the object, so we would integrate the acceleration vector because we know that the integration of acceleration gives us velocity.
On integrating we have
$\vec v = {\vec v_0} + \int\limits_0^t {\left[ {\vec adt} \right]}$
If the body starts from rest, the initial velocity ${\vec v_0}$ is zero, so we're left only with
$\vec v = \int\limits_0^t {\left[ {\vec adt} \right]}$ (2)
Here we can rearrange the equation too and replace Velocity and acceleration will both be on the left-hand side of this equations 1 and 2, which means we can write it as:
$\vec v \propto \dfrac{{\Sigma \vec F}}{m}$
From this relationship, we see that as the magnitude of the net force increases, the velocity will also increase when mass is kept constant,
But the velocity will decrease as the mass increases assuming the same net force.

Note:
Practically this can be seen as when you throw a large stone it goes slow then replace it with a smaller stone and throw it with the same force it will go with a greater speed this proves that speed increases with a decrease in mass.
Then you hit a ball with the greater force it moves with greater velocity thus we can say that more the force or unbalanced force more will be the acceleration