What Causes an Object to Stop after a Collision?

[mike_302]

Homework Statement

Two balls roll directly towards each other. The 0.25kg ball has a speed of 1.7m/s. The 0.18kg ball has speed of 2.5m/s. After the collision, the 0.25kg ball has reversed its direction and has a speed of 0.10m/s . What is the magnitude and direction of the 0.18 kg ball after hte collision?

Homework Equations

P(total)=P'(total)

The Attempt at a Solution

I know the answer... IT's 0 m/s . Further question though:

On a test, I'd be questioning that result. As I did when I first obtained it in the homework... So I thought to myself: Zero tends not to just come out of nowhere... There's usuall an indicator that it's coming. What is the indicator that one of the objects in a collision will stop? Is there any sort of indicator in this case?

Thanks!

Mike

 

[dx]

There's no special indicator in this case other than the momentum conservation calculation.

 

[nlightner]

The indicator that one of the objects in a collision will stop is when the initial momentum of the system is equal to the final momentum of the system. In this case, the initial momentum of the system is the sum of the momentums of the two balls before the collision, and the final momentum is the sum of the momentums of the two balls after the collision. Since the initial momentum is not equal to the final momentum, there must be an external force acting on one of the balls to cause it to stop. This external force could be friction or an impact with another object. Without knowing more information about the specific scenario, it is difficult to determine the exact cause of the 0 m/s result. However, it is important to analyze the situation and consider all possible factors before concluding that one of the objects will stop.