Why are the objects the same speed at the finish line?

In summary, the conversation discusses the concept of net work and its relation to kinetic energy and force of gravity. It is established that the work by force of gravity is the same for both objects, but this does not necessarily mean that they will reach the finish line at the same time. This is because the objects may have different distances to travel. The conversation also touches upon the role of normal force and how it does not do any work due to its perpendicular direction to the displacement. The relationship between force, work, and displacement is also mentioned.
  • #1
Lori
I have the problem below.

I know that net work is equal to the change in kinetic energy which is Wnet= 0.5mv^2-0.5mvi^2.I also know that the work by force of gravity is the same for both objects. I don't understand why the objects would be the same speed at the finish line.
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  • #2
The speed will be the same. This does not mean that they will reach the finish line at the same time, block B has to travel longer.
 
  • #3
Orodruin said:
The speed will be the same. This does not mean that they will reach the finish line at the same time, block B has to travel longer.
Can you explain why this would be the case? Would it be because net work is the same for both objects? Because if that's the case, then KE has to be the same and so the final velocities are the same.

However. I wouldn't know why new work is the same for both objects.
 
  • #4
Lori said:
Would it be because net work is the same for both objects? Because if that's the case, then KE has to be the same and so the final velocities are the same.
Yes.

Lori said:
I wouldn't know why new work is the same for both objects.
You said it yourself in the first post:
Lori said:
I also know that the work by force of gravity is the same for both objects.
 
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  • #5
Orodruin said:
Yes.You said it yourself in the first post:
Ahh yeah. I wasn't sure if force of gravity was the only work done on object but it makes sense since the ramp is frictionless and gravity is the only force applied.
 
  • #6
Lori said:
Ahh yeah. I wasn't sure if force of gravity was the only work done on object but it makes sense since the ramp is frictionless and gravity is the only force applied.
Gravity is not the only force. There is also a normal force from the ramp. Can you figure out why it does no work?
 
  • #7
Orodruin said:
Gravity is not the only force. There is also a normal force from the ramp. Can you figure out why it does no work?
Oh . Well the component in the y direction of gravity balances out normal force. So the normal force doesn't do any work.
 
  • #8
Lori said:
Oh . Well the component in the y direction of gravity balances out normal force. So the normal force doesn't do any work.
It is not really a matter of force equilibrium. Whether a force does work or not depends on the force's component parallel to the displacement.
 
  • #9
Orodruin said:
It is not really a matter of force equilibrium. Whether a force does work or not depends on the force's component parallel to the displacement.
Oh right! I was talking about net work. So the work that normal force does is 0
 

What is the significance of objects having the same speed at the finish line?

The fact that objects have the same speed at the finish line is important because it demonstrates the principles of motion and energy conservation. It shows that all objects, regardless of their initial speed or size, will reach the finish line at the same time if no external forces act upon them.

Why do objects have the same speed at the finish line?

This is due to the law of inertia, which states that an object will remain in its state of motion unless acted upon by an external force. In this case, the objects are not being acted upon by any external forces, so they will continue to move at a constant speed until they reach the finish line.

Does this mean that objects with different initial speeds will reach the finish line at the same time?

Yes, as long as they are not affected by any external forces, objects with different initial speeds will reach the finish line at the same time. This is because their acceleration is constant and they will cover the same distance in the same amount of time.

Are there any exceptions to this rule?

There are some exceptions to this rule, such as when air resistance or friction are present. In these cases, the objects may have different speeds at the finish line due to the external forces acting upon them. However, in a vacuum or a frictionless environment, the rule holds true.

How is this concept applied in real-world scenarios?

This concept is applied in various fields such as physics, engineering, and sports. For example, in sports like running or swimming, athletes strive to maintain a constant speed throughout the race to reach the finish line as quickly as possible. In engineering, this concept is used in designing machines and vehicles to ensure they move at a steady pace. Understanding this concept is crucial in accurately predicting the motion of objects in various scenarios.

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