Impulse and Momentum: Substitution Trouble

In summary, the conversation discusses a problem involving a collision between a van and a car, with given masses and velocities. The problem requires using the concept of momentum and treating velocities as vectors to find the final velocities of both objects. The conversation also suggests using substitution instead of solving for kinetic energy.
  • #1
Sakura
4
0
Ok, in this problem I am getting bogged down in the basic algebra part of it. I had one person explain it once but I still missed something.:frown:

a 1055-kg van, stopped at a traffic light, is hit directly in the rear by a 715-kg car traveling with a velocity of +2.26 m/s. Assume that the transmission of the van is in neutral, the brakes are not being applied, and the collision is elastic. What is the final velocity of (a) the car and (b) the van?
m1 = 715 kg
m2 = 1055 kg
vo1 = +2.25 m/s
vo2 = 0 m/s
vf1 = ?
vf2 = ?
http://www35.websamba.com/aerowenkitten/images/untitled.jpg
 
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  • #2
You know the initial masses and velocities and hence the initial momentum...from this you know the *relative* approach velocity before impact...and as the collision is elastic you also know the relative exit velocity...If you can form 2 equations using this info you should be able to spot a substitution easily...I don't think trying to solve in terms of KE is the best method
 
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  • #3
Think of it this way.

The initial momentum of the system (the car + the van) must equal the final momentum of the system (the car + the van).

Treat velocities as vectors such that -> would be (+) and <- would be (-).

That should help.
 
  • #4
AHHH... thank you! lol makes more sense that way!
 
  • #5
No problem.
 

FAQ: Impulse and Momentum: Substitution Trouble

What is the difference between impulse and momentum?

Impulse is the change in momentum of an object over a period of time, while momentum is the measure of an object's motion and is calculated by multiplying its mass by its velocity.

How is momentum conserved in a closed system?

In a closed system where there is no external force acting on the objects, the total momentum before and after a collision or interaction remains the same. This is known as the law of conservation of momentum.

What is the equation for calculating impulse?

The equation for impulse is impulse = force x time, or J = F x t. This means that the greater the force or the longer the time of impact, the greater the impulse.

What is the meaning of "substitution trouble" in relation to impulse and momentum?

"Substitution trouble" refers to the issue of substituting variables in equations without understanding the underlying concept. In the context of impulse and momentum, this can lead to incorrect calculations and a lack of understanding of how these concepts are related.

How does impulse affect an object's motion?

Impulse causes a change in an object's momentum, which in turn affects its motion. A larger impulse will result in a greater change in momentum and therefore a greater change in an object's motion.

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