How can you tell, based on observing an object, that there is a net force acting upon that object?

Net force is the sum of all forces acting on an object. The net force can be calculated using Newton's second law, which states that F = ma, where: F is the net force. m is the mass of the object.

Explanation:

accelerating

Explanation:

If  accelerating it has a net ( unbalanced) force acting on it .

  with zero net forces it will either remain at rest or continue moving (but not accelerate)

good for her? ? where is the question?

can be answered using momentum.

momentum = p

p1= mass1 * velocity1

p1 = p2

therefore

p1 = 6kg * 4m/s

p1 = 24kgm/s

p2=m2 * v2

24 kgm/s = 7kg * v2

v2 = 24 kgm/s / 7kg

v2= 3.42 m/s