Linear momentum and velocity direction

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Discussion Overview

The discussion revolves around the application of the conservation of linear momentum in problems involving directionality of velocity. Participants explore how to correctly account for the direction of velocity when formulating equations for momentum conservation, particularly in a scenario involving two blocks with the same initial velocity on a frictionless surface.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant emphasizes that momentum is a vector quantity, indicating that direction must be considered in momentum conservation problems.
  • Another participant reiterates the necessity of accounting for direction, suggesting that initial velocities should be treated as +v0 and -v0.
  • A participant cautions against making assumptions about the directions of velocities after a collision, proposing that v1 and v2 should be treated as unknowns to be solved for.

Areas of Agreement / Disagreement

Participants generally agree on the importance of considering direction in momentum conservation, but there is no consensus on the specific formulation of the equations presented.

Contextual Notes

Participants note that the initial velocities are not simply v0 but should include directional components, which may affect the equations used in momentum conservation.

metallica007
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Hi everyone
When using the concept of the conservation of the linear momentum ΣPi = ΣPf to solve a problem, should I consider the the direction of the velocity? For Example, the following problem
t9870n.jpg

which one of the following equations is correct?
m1v0+m2v0=m1v1+m2v2
or
m1v0-m2v0=-m1v1+m2v2
note: both of the blocks have the same intial velocity (v0) because the surface is frictionless.
 
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Momentum is a vector quantity, so you absolutely do have to pay attention to the direction when solving problems with conservation of momentum.
 
metallica007 said:
When using the concept of the conservation of the linear momentum ΣPi = ΣPf to solve a problem, should I consider the the direction of the velocity?
As cjl already stated, you must take direction into account.

which one of the following equations is correct?
m1v0+m2v0=m1v1+m2v2
or
m1v0-m2v0=-m1v1+m2v2
note: both of the blocks have the same intial velocity (v0) because the surface is frictionless.

Careful here. You're really using v0 as the initial speed; the initial velocities are +v0 and -v0. After the collision I would not make any assumptions about the directions; just let v1 and v2 be the velocities, which you'll solve for.
 
Thank you very much guys :)
 

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