Elastic and inelastic collisions
- Intro Lesson: a7:19
- Intro Lesson: b3:35
- Intro Lesson: c3:52
- Lesson: 1a2:41
- Lesson: 1b1:58
- Lesson: 2a9:13
- Lesson: 2b6:53
- Lesson: 2c13:23
Elastic and inelastic collisions
Lessons
In this lesson, we will learn:
- Meaning of elastic and inelastic collisions
- What happens to kinetic energy in a collision?
- Understanding perfectly inelastic collisions
- Problem solving with elastic and inelastic collisions
Notes:
- Total momentum and total energy are conserved in collisions. However, kinetic energy is not always conserved, since it can be converted into other forms of energy.
- Elastic collision: collision where no kinetic energy is lost
- Inelastic collision: collision where part of the kinetic energy is converted to other forms of energy
- Perfectly inelastic collision: collision where the maximum possible amount of kinetic energy is converted to other forms of energy; objects stick together.
Conservation of Momentum
∑pi=∑pf
pi: initial momentum, in kilogram meters per second (kg·m/s)
pf: final momentum, in kilogram meters per second (kg·m/s)
Conservation of Energy
∑Ei=∑Ef
Ei: initial energy, in joules (J)
Ef: final energy, in joules (J)
Kinetic Energy
KE=21mv2
KE: kinetic energy, in joules (J)
m: mass, in kilograms (kg)
v: speed, in meters per second (m/s)
Potential Energy
PE=mgh
PE: potential energy, in joules (J)
g: acceleration due to gravity, in meters per second squared (m/s2)
h: height, in meters (m)
- IntroductionIntroduction to elastic and inelastic collisionsa)Meaning of elastic and inelastic collisionsb)What happens to kinetic energy in a collision?c)Understanding perfectly inelastic collisions
- 1.Solving word problems with momentum and elastic/inelastic collisionsa)Two cars collide head-on and stick together. The cars are stationary after colliding.
- Is total momentum conserved?
- Is total energy conserved?
- Is the collision elastic or inelastic?
b)Identify each situation as an inelastic or elastic collision.
- One car crashes into another, bouncing apart with a loud bang.
- A hammer strikes a piece of steel, bouncing off and producing sparks.
- A He atom collides with a H atom, bouncing off and maintaining overall kinetic energy.
- 2.∑Ei=∑Ef ; ∑pi=∑pf: Conservation of energy and momentum in elastic and inelastic collisionsa)3.6×104 kg train car A travelling at 5.40 m/s [E] collides with stationary 5.20×104 kg train car B. The train cars bounce apart, and after the collision, train car A travels at 1.70 m/s [E]. Determine if this collision is elastic or inelastic.b)0.50 kg steel ball A travelling [E] with a kinetic energy of 0.49 J collides with stationary 0.75 kg steel ball B head-on. After the collision, ball A travels at 0.28 m/s [W]. Assuming the collision is elastic, find the velocity of ball B after the collision.c)A "ballistic pendulum" is a method used to measure the velocity of a bullet. A 5.60 g bullet is fired at a 1.24 kg wooden block suspended as shown in the diagram, and the block rises to 0.250 m higher than its initial position at the peak of its swing.
- Find the velocity of the bullet when it hits the block.
- Calculate how much of the kinetic energy is lost in this inelastic collision. Explain what happens to this energy.