# Momentum question, seems easy, y can't I get it

• lala56
In summary, the conversation discusses a scenario of a 10.0 g marble colliding with a larger 25.0 g marble on a frictionless surface. The objective is to calculate the change in kinetic energy for each marble after the collision. The method of finding the change in kinetic energy is correct, but a more accurate value for the final speed should be used.
lala56
"A 10.0 g marble slides to the left with a velocity of magnitude 0.600 m/s on the frictionless, horizontal surface of an icy, New York sidewalk and has a head-on elastic collision with a larger 25.0 g marble sliding to the right with a velocity of magnitude 0.250 m/s (Fig. 8.35)."

I need to "Calculate the change in kinetic energy (that is, the kinetic energy after the collision minus the kinetic energy before the collision) for each marble."

So, I will start with the 25g marble going right, which hits the 10g marble and revserses direction to go left

I correctly found the velocity of the 25g marble after the collision, it is -.24.
Now, to find the change in kinetic energy, i did this:

v1=intial velocity
K2-K1=.5mv^2 - .5mv1^2

.5(.025)(-.24)^2 - .5(.025)(.25)^2

isn't this how one is supposed to find change in kinetic energy? Then why is it incorrect? did i go wrong with the positive negative sign?

this one should be negative right?

thankyou

Your method is correct, but since initial and final speeds are so close I would suggest using a more accurate value for the final speed than -.24 m/s when calculating the change in KE. You can always round it off later.

## 1. What is momentum?

Momentum is a physical quantity that measures the motion of an object. It is calculated by multiplying the mass of an object by its velocity.

## 2. How is momentum different from velocity?

Velocity is a measure of an object's speed and direction, while momentum takes into account the mass of the object as well. Two objects can have the same velocity but different momentum if they have different masses.

## 3. Why is momentum important?

Momentum is important because it helps us understand how objects move and interact with each other. It is also a conserved quantity, meaning it remains constant unless acted upon by an external force.

## 4. How is momentum conserved in a closed system?

In a closed system, the total momentum before an interaction or event is equal to the total momentum after the event. This is known as the law of conservation of momentum.

## 5. How can momentum be calculated?

Momentum can be calculated by multiplying the mass of an object by its velocity. The formula for momentum is p = m x v, where p is momentum, m is mass, and v is velocity.

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