Engineering Physics help (Frictionless surface with hockey puck)

In summary, the conversation discusses a figure from an engineering physics book where a frictionless puck is given a hammer blow on a level air table. The trajectory of the puck after the blow is delivered will depend on the angle of the blow. The final velocity of the puck will be greater than the initial velocity due to the vertical component of the bump. The velocity of the puck will remain constant in both magnitude and direction as there are no external forces acting on it.
  • #1
This is an example from my engineering physics book which didn't have an answer at the end of the book,
This figure is a snapshot looking down on a frictionless puck moving at uniform velocity from left to right on a level air table. At the position shown, the puck is given a short, sharp hammer blow B in a direction perpendicular to that in which it is initially moving.

0=puck ( Please ignore parentheses in picture they are there to help aligh picture)

-------------------- 0 ------------------
((()))))))))))))))))))))^ Vi---->

A) Show on the figure a trajectory that the puck might follow on the table after the blow is delivered?

My answer - The puck would go exactly 45 degrees to the right (I am not entirely sure - I keep on thinking it is going to go straight)

B) Will the final speed Vi of the puck (immediately after the blow) be equal to, greater than, or smaller than Vi? Explain your reasoning?

My answer - equal to because on a frictionless surface the velocity is never going to change

C) How will the velocity of the puck on the frictionless surface behave as time goes by after the blow? That is, will either the magnitude or the direction of the velocity (or both) keep on changing? If so, how?

My answer = ? (baffled on this part)

I am not sure if my answers are right. I need help understanding the third part for sure. Please correct me if I am wrong for my answers a and b.
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  • #2
A) The trajectory will indeed be deviated. However, the angle it will make will be dependend on the "bump". If it is so that the vertical speed is exactly the same as the horizontal speed, then yes, it will give a 45° angle

B) I'm assuming you are familiar with the fact that speed is a vector. Since the bumpt is perpendicular to the traveling speed, the horizontal speed will not change. The vertical speed however, will differ from zero. Hence, V=Vx+Vy, the end velocity will be greater then the begin velocity. Your reasoning is wrong, because while it is true that the velocity will not decrease due to friction, it may increase due to collisions (like the bump)

C) Since there are no forces acting on the puck after the bump, there is no acceleration and the velocity will remain constant, both in magnitude and direction.

Hope it helps :smile:
  • #3

Your answers for parts A and B are correct. For part C, the magnitude and direction of the velocity will remain constant after the blow is delivered. This is because there is no friction on the surface to slow down the puck or change its direction. The hammer blow only changes the direction of the puck, but does not affect its speed. Therefore, the puck will continue to move at a constant velocity in a straight line after the blow.

1. What is frictionless surface in the context of engineering physics?

A frictionless surface is a hypothetical surface that has no resistance or friction when an object moves across it. In reality, all surfaces have some degree of friction, but in engineering physics, a frictionless surface is often used as an idealized scenario to simplify calculations and understand the fundamental principles of motion.

2. How does a frictionless surface affect the movement of a hockey puck?

On a frictionless surface, a hockey puck will continue moving in a straight line with a constant velocity unless acted upon by an external force. This is due to the absence of any resistance or friction that would normally cause the puck to slow down or change direction.

3. What are the practical applications of studying frictionless surfaces in engineering physics?

Understanding the principles of motion on a frictionless surface is crucial in many fields of engineering, such as designing efficient machines and transportation systems. It also helps in developing strategies for reducing friction and increasing efficiency in various industrial processes.

4. How is the coefficient of friction related to a frictionless surface?

The coefficient of friction is a measure of the amount of resistance or friction between two surfaces. In a frictionless surface, the coefficient of friction is zero, as there is no resistance between the surfaces. However, it is still a useful concept in engineering physics for understanding the effects of friction on an object's motion.

5. Can a frictionless surface exist in real life?

No, a completely frictionless surface does not exist in reality. However, scientists and engineers can come close to creating a frictionless environment by using specialized materials and techniques, such as using superconductors or reducing the surface roughness of objects.

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