How Do You Calculate the Mass of a Cart in a Momentum Problem?

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Homework Help Overview

The problem involves a scenario where a boy jumps onto a cart, and the goal is to determine the mass of the cart using principles of momentum. The context includes known masses and velocities, with the cart initially at rest.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • The original poster attempts to identify relevant equations and concepts, such as acceleration and forces, but expresses uncertainty about how to proceed. Some participants hint at the conservation of momentum as a key principle to consider during the collision.

Discussion Status

Participants are exploring the implications of the net force being zero and discussing the conservation principles that apply to the scenario. There is an indication of guidance being offered, but no consensus has been reached on the specific approach to take.

Contextual Notes

The original poster notes a lack of clarity on how to apply known values and concepts, such as acceleration and forces, in the context of the problem. There is also mention of potential confusion regarding the direction and application of kinematics equations.

helen3743
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Thank you--

Problem:
A 50 kg boy runs at a speed of 10 m/s and jumps onto a cart. The cart is initially at rest. If the speed of the cart with the boy on it is 2.50 m/s, what is the mass of the cart?

I don't know what to do. This probelem seems very simple but I don't know where to start.

These I know are the knowns:
vo(cart) = 0 m/s
vf(cart) = 2.50 m/s
vo(boy) = 10 m/s
vf(boy) = 2.5 m/s

So I know velocities and I know the mass of the boy.
Should I start off by finding the acceleration from F=ma, since I know a mass? But then I don't know how to find F. I know Fn = mg in the y component, but I don't know what I would use Fn next for. Am I supposed to use kinematics equations? But I don't know a, x, or time. Direction is needed, thanks!
 
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It's much simpler than you think. Hint: What's conserved when the boy "collides" with the cart?
 
Sum of external forces = 0! thank you!
 
SO yeah, the net force is zero. This clue leads us to what principle pf physics, you know, with its own set of silly equations and all.
 
DaMastaofFisix said:
SO yeah, the net force is zero. This clue leads us to what principle pf physics, you know, with its own set of silly equations and all.

Care to expand / explain your comment DaMasta? Edit. perhaps this is best discussed in the pf lounge actually.

~H
 
Last edited:

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