How to Calculate Average Force of a Proton Passing Through a Metal Film

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Homework Help Overview

The problem involves calculating the average force experienced by a proton as it passes through a metal film, given its initial and final speeds and the thickness of the film. The subject area includes concepts from mechanics and energy conservation.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • The original poster attempts to apply kinetic energy and momentum equations but expresses confusion about the expected direction of the force and the relevance of gravitational effects. Some participants suggest using conservation of energy, while others propose using equations of motion to find acceleration and subsequently force.

Discussion Status

Participants are exploring different methods to approach the problem, including the Work-Energy Theorem and equations of motion. There is no explicit consensus on the best approach, but multiple lines of reasoning are being discussed.

Contextual Notes

Participants note that gravitational effects can be ignored due to the small mass of the proton, and there is uncertainty regarding the interpretation of the force's direction.

Chica1975
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Homework Statement


a proton (m= 1.67 x 20E027kg) that has a speed of 5.0 x 10E6m/s passes thru a metal film of thickness 0.010mm and emerges with a speed of 2.0 x 10E6m/s. how large an average force opposed its motion thru the film?



Homework Equations



KE=.5mvE2
P=mv (momentum)

The Attempt at a Solution


I tried to plug the above equations and nothing works. to be honest I am completely lost. What am I to do? the answer suggests that the force is going N - why if its opposing and its going thru the film it should be going in the opposite direction? Do I use gravity - I have no idea what is expected of me or what they are asking in the first place.

Please help me!
 
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You can ignore gravitational effects since the mass is quite small.

However, you can apply conservation of energy and easily solve this problem.
 
An alternative to the above:

You know the initial speed, the final speed and the distance travelled.

Plug that into one of the equations of motion and you'll get the acceleration.

From that you can use F=ma to get the force.
 
The Work-Energy Theorem:

Wnet = Δ(KE) .

In this case, Wnet = Favg·x .
 

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