How Does Conservation of Momentum Determine Speed After a Collision?

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Homework Help Overview

The discussion revolves around a problem involving conservation of momentum in a collision scenario where a woman jumps onto a skateboard. The participants are exploring how to calculate the combined speed of the woman and skateboard after the collision.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants are attempting to apply the linear momentum equation and are questioning their calculations. Some are exploring the concept of conservation of momentum and its implications for the problem setup.

Discussion Status

There is an ongoing exploration of the correct application of momentum principles. Some participants are providing guidance on the conservation of momentum concept, while others are reflecting on their previous calculations and assumptions.

Contextual Notes

Participants are grappling with the initial conditions of the problem, including the mass and velocity of the woman and skateboard, and are questioning the assumptions made about the skateboard's initial velocity.

Crichar1
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A woman with a mass of 44 kg runs at a speed of 8 m/s and jumps onto a giant 30 kg skateboard initially at rest. What is the combined speed of the woman and the skateboard?

44 kg / 8 m/s=5.5
30 kg / 8m/s=3.75

5.5+3.75=9.25m/s
 
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What do you know about mechanics that will help? Any equations?

The Bob
 
Think momentum.
 
i tried the linear momentum equation..mass * velocity and the answer was still incorrect
 
But what did you do to get this incorrect answer?

The Bob
 
mass x velocity

44kg x 8m/s= 352

30kg x 8m/s=240

352-240=112m/s

didn't seem right but i thought i would try it anyways
 
Right, now I see what you're doing. Have you heard of something called 'conservation of momentum'? Basically, the momentum before a 'change' must be equal to the combined momentum afterwards. You've, therefore, wrongly assumed that the skateboard has velocity of 8ms-1.

So... try imagining the woman and the skateboard as one mass after they have 'combined'.

The Bob
 
Crichar1 said:
i tried the linear momentum equation..mass * velocity and the answer was still incorrect

Conservation of momentum. The total momentum before she jumps on the board=total momentum after she jumps on the board.
 

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