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AP Physics: Newton's Laws of Motion Conceptual Questions


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Why does a child in a wagon seem to fall backward when you give the wagon a sharp pull forward?
When you pull the wagon sharply forward, the child is trying to maintain its position/ state of motion = inertia therefore meaning that she would jolt backward trying to do so after the sharp pull forward.
If an object is moving, is it possible for the net force acting on it to be zero?
Yes, this is possible. When an object is moving at constant velocity there is no net force acting on it. When an object is inconstant, there is a net force.
If the acceleration of an object is zero, are no forces acting on it?
If there is no acceleration there can still be forces acting on the object. There can still be forces like force of gravity, normal force, static friction and others. However, there is the distinction between there being no acceleration and if there no net forces. If there is no acceleration there is no net forces because of the
F = ma equation.
You pull a box with a constant force across a friction less table using an attached rope held horizontally. If you now pull the rope with the same force at an angle to the horizontal, does the acceleration of the box increase, decrease or stay the same?
The acceleration will decrease. If you are pulling something at an angle with the same force that you would've pulled something to the horizontal means that the horizontal component of that angled force is lesser than the force solely pulled at the horizontal. Therefore, being that the two situations use the same object to compensate to reach the same force, the acceleration of the second situation would have to be lesser than the first.
When you stand still on the ground. How large a force does the ground exert on you? Why doesn't this force make you rise up into the air?
When you are standing still, your mass is accelerating due to gravity meaning you have weight. There is an equal and opposite force to your force of gravity. This being normal force, perpendicular to you and the surface. You do not rise up into the air because the force of gravity and the normal force balance each other out meaning no net force meaning no change in motion. Newton's First Law of Motion.
Is mass a vector?
No, mass is not a vector. It only has magnitude. However, weight is a vector because it has magnitude and a direction.
What is the unit for one Newton?
kg * m/s^2