Solving for Missing Values in 1D Collision w/v2 ≠ 0

[LilRubyKinz]

Homework Statement

I am in grade 12 physics and I need to prepare for a test; I am looking for a specific type of question to solve but do not have that available to me.

Relevant Equations

N/A

My teacher wants me to know how to solve for missing values in a 1D collision when v2 does NOT equal 0.

Could someone do me a huge favour and make me a practice question to solve for a missing value when v2 does not equal 0? Or even point one out to me online?

And then let me try it out and see if I get it right? It would be a big help to have one as soon as possible. Thanks!

I might need help determining equations to use - but I’ll get around to that. Thank you in advance!

 

[berkeman]

It's best to start with the Relevant Equations that you think would be applicable. What are those equations, and how are they different for elastic versus non-elastic equations?

 

[LilRubyKinz]

It's best to start with the Relevant Equations that you think would be applicable. What are those equations, and how are they different for elastic versus non-elastic equations?

Okay, I was absent for this lesson. So mind any inaccuracies.

I have:

v1 + v1’ = v2 + v2’

m1v1 + m2v2 =m1v1’ + m2v2’

v1’ = [(m1 - m2)/(m1 + m2)]v1

v2’ = [(2m1)/(m1 + m2)]v1

One and two are for elastic systems only I believe? The last two equations don’t involve v2 so I don’t know that they apply here?

 

[LilRubyKinz]

While I’m here - Young’s modulus is also on this test. Does anyone have an idea of what is being asked of this question? Where does mass apply?

 

[berkeman]

Does anyone have an idea of what is being asked of this question?

We're not going to be able to help when you post 1/4 of the page you wrote on, and are not posting the complete Problem Statement and showing your work. We'd really like to help, but you know...

 

[LilRubyKinz]

No that’s the complete statement. The rest of the page is something separate (different assignment).

I’d like to attempt it... but I don’t know what to attempt!

 

[haruspex]

While I’m here - Young’s modulus is also on this test. Does anyone have an idea of what is being asked of this question? Where does mass apply?

You are being asked to calculate the mass of the object that was suspended from the wire to cause the wire to lengthen by the given fraction. If you have no idea how to do that look up Young's modulus in Wikipedia.

 

[haruspex]

Okay, I was absent for this lesson. So mind any inaccuracies.

I have:

v1 + v1’ = v2 + v2’

m1v1 + m2v2 =m1v1’ + m2v2’

v1’ = [(m1 - m2)/(m1 + m2)]v1

v2’ = [(2m1)/(m1 + m2)]v1

One and two are for elastic systems only I believe? The last two equations don’t involve v2 so I don’t know that they apply here?

Well, it isn't much use knowing standard equations if you don't know what all the variables mean and the context in which each equation applies.
Yes, the first is only for perfectly elastic collisions. There is a variant for imperfect elasticity that involves the coefficient of restitution.
The second is conservation of linear momentum. It applies so long as no external force acts.

You can deduce the first equation by combining the second with conservation of mechanical energy (which is conspicuous by its absence from your list). You need to be careful not to assume energy is conserved. The question should make it clear when that is the case.

The last two look like they only apply in special cases, like v2 being zero, say. Ignore them. You can derive them from more general equations as needed. That's better than trying to remember so many equations that you forget when which applies.

 

[LilRubyKinz]

You are being asked to calculate the mass of the object that was suspended from the wire to cause the wire to lengthen by the given fraction. If you have no idea how to do that look up Young's modulus in Wikipedia.

I know Young’s Modulus, but mass is not a variable involved in the formula?

 

[haruspex]

I know Young’s Modulus, but mass is not a variable involved in the formula?

We are not here considering the mass of the wire.
The weight of the attached mass exerts a force on the wire. This is countered by an equal and opposite force at the other end of the wire. This pair of forces produces tension (tensile stress) along the wire.
What does the formula say about stress?