Force and Motion (net force)

[Kalie]

The 'net force' in the statements below is the sum of ALL forces acting on the body.

During the collision of a car with a locomotive, the locomotive exerts an equal size force on the car as the car exerts on the locomotive.
False

If an object's speed does not change, no net force is acting on the object.
False, there is a net force of zero

If two objects have the same acceleration, they are under the influence of equal forces.
False, F=ma they can have a different mass and thus a different force

The net force which acts on an object which maintains a constant velocity is zero.
True

If a net force acts on an object, the object's velocity will change.
False, the net force acting on the object can be zero

A truck initially moving at a constant velocity will slow down unless a small net force is applied.
False, the trucks velocity will only change if the net force is not zero


This is what I figured out on my own, but I am told it is incorrect. Could someone tell me what I am doing wrong?

 

[cristo]

The 'net force' in the statements below is the sum of ALL forces acting on the body.

During the collision of a car with a locomotive, the locomotive exerts an equal size force on the car as the car exerts on the locomotive.
False

What's your reasoning for this answer?

If an object's speed does not change, no net force is acting on the object.
False, there is a net force of zero

Well, no net force is equivalent to saying a net force of zero. However, note the use of the word speed in this question. An object can accelerate whilst retaining a constant speed (c.f. circular motion). So, your answer of false is correct, but not for the reason you give.

If two objects have the same acceleration, they are under the influence of equal forces.
False, F=ma they can have a different mass and thus a different force

Correct

The net force which acts on an object which maintains a constant velocity is zero.
True

If a net force acts on an object, the object's velocity will change.
False, the net force acting on the object can be zero

Again, "a net force" means "a non-zero net force"

A truck initially moving at a constant velocity will slow down unless a small net force is applied.
False, the trucks velocity will only change if the net force is not zero

Correct.

This is what I figured out on my own, but I am told it is incorrect. Could someone tell me what I am doing wrong?

 

[m2003]

Your responses are mostly correct, but there are a few things that could be clarified or expanded upon:

1. During the collision of a car with a locomotive, the locomotive exerts an equal size force on the car as the car exerts on the locomotive.
False - This statement is not completely accurate. In a collision, the force exerted by each object on the other will depend on their respective masses and velocities. The forces may be equal in size, but they may not necessarily be the same.

2. If an object's speed does not change, no net force is acting on the object.
False - This statement is also not completely accurate. If an object's speed is constant, it means that the net force acting on it is zero. However, there may still be individual forces acting on the object, but they are balanced and cancel out, resulting in a net force of zero.

3. If two objects have the same acceleration, they are under the influence of equal forces.
False - As you correctly stated, the force acting on an object is equal to its mass multiplied by its acceleration (F=ma). Therefore, two objects with the same acceleration may have different masses and thus different forces acting on them.

4. The net force which acts on an object which maintains a constant velocity is zero.
True - This statement is correct. If an object is moving at a constant velocity, it means that the net force acting on it is zero, as all the individual forces acting on it are balanced and cancel out.

5. If a net force acts on an object, the object's velocity will change.
False - This statement is not entirely accurate. If there is a net force acting on an object, its velocity will change according to the equation F=ma. However, if the net force is zero, the object's velocity will remain constant.

6. A truck initially moving at a constant velocity will slow down unless a small net force is applied.
False - This statement is not completely accurate. If a truck is moving at a constant velocity, it will continue to do so unless a net force is applied to change its velocity. If no net force is applied, the truck will continue to move at a constant velocity.