Confirming an observation about Newton's Laws

In summary, when dealing with a frictionless inclined plane and knowing the velocity of an object going up the plane, it is safe to say that the velocity will be the same on the way back down due to the conservation of mechanical energy. This is also true for objects tossed upward, as the speed will remain the same when falling back down. However, it should be noted that it is the speed that remains constant, not the velocity, as the direction of motion is reversed.
  • #1
frankfjf
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When approaching a problem concerning Newton's 2nd law of motion, if I'm dealing with a frictionless inclined plane and know the velocity of an object going up the plane, is it safe to say that the velocity will be the same on the way back down since no friction is present?
 
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  • #2
This is of course assuming that the object, such as a block, is projected up the plane then allowed to slide back down, and I know the velocity it used to go up the incline.
 
  • #3
frankfjf said:
is it safe to say that the velocity will be the same on the way back down since no friction is present?
Yes, since mechanical energy is conserved. For the same reason, if you toss a ball upward at some speed, when it falls back down it will have the same speed (ignoring air resistance). (Nitpick: Of course it's the speed that's the same, not the velocity, since the direction of motion is reversed on the way down.)
 
  • #4
Edit: Darn it DocAl, I was answering this one! Well, this is what I wrote:

Yes (I assume you meant that the final speed at the bottom will be the same as the initial speed as it starts up the incline). Since there is no friction, the only the componant of the weight that is parallel to the surface will act. This means, if the plane is at a constant angle, the acceleration will be a constant g(sin theta), where theta is the angle of incline. Also, from an energy point of view, since no frictional forces are present, mechanical energy is conserved.
 

1. What are Newton's Laws of Motion?

Newton's Laws of Motion are three physical laws that describe the behavior of objects in motion. They were first published by Sir Isaac Newton in 1687 in his book "Philosophiæ Naturalis Principia Mathematica".

2. How do Newton's Laws of Motion affect everyday life?

Newton's Laws of Motion explain how objects move and interact with each other in everyday situations. For example, they can help us understand why objects fall to the ground, why it is difficult to stop a moving object, and how a rocket can travel through space.

3. How do you confirm an observation about Newton's Laws of Motion?

To confirm an observation about Newton's Laws of Motion, you can conduct experiments and gather data to test the laws. The data should support the predictions made by the laws in order to confirm their validity.

4. Can Newton's Laws of Motion be broken?

No, Newton's Laws of Motion are fundamental principles of physics and have been confirmed through countless experiments and observations. However, they may not always accurately describe the behavior of objects in extreme circumstances, such as at the speed of light or on a quantum level.

5. What is the difference between Newton's First, Second, and Third Law of Motion?

Newton's First Law of Motion states that an object will remain at rest or in constant motion unless acted upon by an external force. Newton's Second Law of Motion explains how the motion of an object changes when a force is applied to it. Newton's Third Law of Motion states that for every action, there is an equal and opposite reaction.

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