An object will remain at rest or in uniform motion in a straight line unless acted upon by an external force.
Newton's Second Law: Law of Action
The acceleration of an object is dependent upon two variables - the net force acting upon the object and the mass of the object
Newton's Third Law: Law of Motion
For every action, there is an equal and opposite reaction.
The soccer ball will stay still and in place until acted upon by the figure with a greater force when it will be moved in the direction the most force was applied. The ball will not stop once in motion unless acted upon by an other external force such as the net.
If the man used x amount of force to push the car (which assumable weighs less than the firetruck) and the car moved and then used the same force on the truck, the truck would not move because it has a larger mass.
When the girl pushes off the boat, she pushes herself towards the water as well as pushes the boat away from her. As an equal and opposite reaction.