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Average Force

  • Thread starter Chica1975
  • Start date
  • #1
63
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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!
 

Answers and Replies

  • #2
rock.freak667
Homework Helper
6,230
31
You can ignore gravitational effects since the mass is quite small.

However, you can apply conservation of energy and easily solve this problem.
 
  • #3
2,685
20
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.
 
  • #4
SammyS
Staff Emeritus
Science Advisor
Homework Helper
Gold Member
11,304
998
The Work-Energy Theorem:

Wnet = Δ(KE) .

In this case, Wnet = Favg·x .
 

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