Calculating Mass in a Momentum Conservation Problem

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In summary, the conversation discussed the concept of conservation of momentum in a collision between two runners. It was determined that in order for the runners to come to a complete stop, their initial momenta must be equal and opposite, which can only happen if they have the same mass. It was also mentioned that the runners may or may not bounce off each other, but momentum will always be conserved.
  • #1
javas1
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Homework Statement


A runner has a mass of 168 Kg and is traveling North at 5 meters per second. Another runner is traveling South at 5 meters per second. They collide and come to a complete stop. What is the mass of the second runner



Homework Equations



I do not have an equation.


The Attempt at a Solution



I have stayed up all night trying searching on the Web to find out anything.
 
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  • #2
Hint: What's conserved in any collision?
 
  • #3
Yes, it is momentum, I believe.

I read that if two objects crash into each other, then they bounce off each other - and that is not a complete stop.
However, it seems that the mass of both objects would need to be equal, as long as the velocity is equal.

Is that right?
 
  • #4
I think that's right. If one was 200lbs then that one would blow through the other guy and not stop at the point of collision like i think the question is saying.
 
  • #5
sean-820 said:
I think that's right. If one was 200lbs then that one would blow through the other guy and not stop at the point of collision like i think the question is saying.


Unless the other guy was also 200 lbs, right?
 
  • #6
javas1 said:
Yes, it is momentum, I believe.
Right.

I read that if two objects crash into each other, then they bounce off each other - and that is not a complete stop.
They may or may not bounce off, but no matter what, momentum will be conserved. Here you are told that they come to a stop, so you know they don't bounce off.
However, it seems that the mass of both objects would need to be equal, as long as the velocity is equal.

Is that right?
Yes, exactly right. Since they come to a complete stop, you know that the total momentum is zero. That can only be true if their initial momenta are equal and opposite. Since they have the same speed, the only way they can have the same momentum is if they have the same mass.
 
  • #7
Doc Al said:
Right.


They may or may not bounce off, but no matter what, momentum will be conserved. Here you are told that they come to a stop, so you know they don't bounce off.

Yes, exactly right. Since they come to a complete stop, you know that the total momentum is zero. That can only be true if their initial momenta are equal and opposite. Since they have the same speed, the only way they can have the same momentum is if they have the same mass.

That's perfect. Thanks!
 

What is the definition of mass?

Mass is a measure of the amount of matter in an object.

How do you calculate the mass of an object?

To calculate the mass of an object, you can use the formula: mass = density x volume. You can also use a scale or balance to measure the mass directly.

What is the unit of measurement for mass?

The unit of measurement for mass is typically expressed in grams (g) or kilograms (kg). In some cases, it may also be measured in pounds (lbs) or ounces (oz).

Can mass change?

Yes, mass can change depending on the amount of matter present in the object. For example, if you add more material to an object, its mass will increase. However, the mass of an object will always remain the same regardless of its location or the Earth's gravitational pull.

What is the difference between mass and weight?

Mass and weight are often used interchangeably, but they are actually two different concepts. Mass is a measure of the amount of matter in an object, while weight is a measure of the force of gravity acting on an object. This means that an object's mass will remain the same regardless of its location, but its weight may change depending on the strength of the gravitational pull. Mass is measured in grams or kilograms, while weight is measured in newtons (N) or pounds (lbs).

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