Calculating Momentum and Speed: IGCSE Forces and Motion Textbook Example

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Homework Help Overview

The discussion revolves around a physics problem related to momentum and speed, specifically within the context of forces and motion as outlined in an IGCSE textbook. The original poster presents a scenario involving an object, Alpha, with given velocities at two different times and a mass that is a multiple of a proton's mass.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • Participants explore the application of the momentum principle, questioning how to rearrange equations without specific mass values. There is discussion about the implications of not knowing the masses involved and whether arbitrary values can be used as long as the mass ratio is maintained.

Discussion Status

The conversation is ongoing, with participants providing guidance on how to manipulate the equations. Some express uncertainty about deriving a value for velocity due to missing mass information, while others encourage further exploration of the equations.

Contextual Notes

Participants note the challenge of working with unknown masses in the equations, which affects their ability to solve for velocity. The discussion reflects a learning environment where assumptions and definitions are being critically examined.

SuchBants
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Homework Statement


V of Alpha at T1 = 10^7
V of Alpha at T2 = 0.6 x 10^7
Mass of Alpha = 4x mass of proton

Homework Equations


P=MV
P1 = P2

The Attempt at a Solution


Bear in mind that I am a year 11 IGCSE student. This is from the textbook at the end of the chapter of forces and motion detailing simple momentum and speed equations.
I've tried many solutions that produce varied results for me.
SAM_1080~2.JPG
 
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Can you show us what you have obtained and explain why you think it is incorrect?
 
I could only ever get as far as arranging the equation using the principle that Momentum before = momentum after. But as I have no values for the masses I found I could not rearrange.
p1= 4m x 107
P2= (4m x107x0.6) + (m x V)
P1 = P2

As you can see I'm stumped here.
 
SuchBants said:
I could only ever get as far as arranging the equation using the principle that Momentum before = momentum after. But as I have no values for the masses I found I could not rearrange.
p1= 4m x 107
P2= (4m x107x0.6) + (m x V)
P1 = P2

As you can see I'm stumped here.
You just need to continue. In that last equation, substitute P1 and P2 using the other equalities you have, and try and find and equation for V.
 
But surely it would be impossible to get a value for V ? Given that we don't know the mass of m or 4m.
 
SuchBants said:
But surely it would be impossible to get a value for V ? Given that we don't know the mass of m or 4m.
Write out the equations and see what happens.
 
20151111_181250-1-1.jpg
Sorry for the late reply.

I reached an answer and my working is attached.
Is it okay to presume M as any number? As long as the ratio of the mass stays 4:1?
 

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