Calculating Collision Speed: Momentum or Kinetic Energy?

In summary, the question is whether to use kinetic energy's equation or momentum's equation to calculate the speed of the lighter object in a collision with a heavier object. The answer is that both equations can be used, but it may be easier to use conservation of momentum in most cases.
  • #1
2sin54
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Hi. Sorry if this looks too beginner-ish question.

Lets say we have two objects moving towards each other. One is heavier than another and we know it's speed. We want to find out how fast should lighter object move so that after the collision both objects would stop.

Question is, what should we use to calculate the speed of the lighter body, kinetic energy's equation or momentum's? Those two give slightly different answers.

Thank you.
 
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  • #2
If you want the objects to stop after they collide, the total momentum must be zero. Kinetic energy will not be conserved, since the collision must be inelastic. (Momentum is always conserved.)
 
  • #3
Momentum is always conserved and total energy is always conserved, so you can use either one in principle. But total energy includes kinetic energy, heat energy lost due to friction, potential energy, etc. so it is easier in many problems to use conservation of momentum. Note that if there are enough unknowns, you may need to use both conservation of energy and momentum.
 
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FAQ: Calculating Collision Speed: Momentum or Kinetic Energy?

What is the difference between momentum and kinetic energy?

Momentum and kinetic energy are both measures of an object's motion, but they are calculated differently and have different physical meanings. Momentum is the product of an object's mass and velocity, while kinetic energy is the energy an object possesses due to its motion.

Which one is more important in determining the motion of an object?

Momentum and kinetic energy both play important roles in determining the motion of an object. However, momentum is typically considered more important because it takes into account the object's mass and velocity, while kinetic energy only considers its velocity.

How are momentum and kinetic energy related?

Momentum and kinetic energy are related by the equation KE = 1/2 mv2, where m is the mass of the object and v is its velocity. This means that as an object's velocity increases, its kinetic energy increases, and its momentum also increases.

Which one is conserved in a closed system?

In a closed system, both momentum and kinetic energy are conserved. This means that the total momentum and kinetic energy of all objects in the system remains constant, even if individual objects may experience changes in momentum and kinetic energy.

What are some real-life examples of momentum and kinetic energy?

Some examples of momentum in everyday life include a moving car, a swinging pendulum, and a thrown ball. Examples of kinetic energy include a moving roller coaster, a basketball being dribbled, and a person running. Both momentum and kinetic energy are essential concepts in understanding the motion and behavior of objects in our world.

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