LIM - Conservation of Momentum

Conservation of Momentum

When two objects collide, the collision can be elastic or inelastic. An elastic collision is one where both the momentum and the kinetic energy are conserved. All other collisions are considered to be inelastic. A perfectly inelastic collision is one where the two objects collide and stick together. Momentum is conserved in an inelastic collision, but kinetic energy is not. If the collision occurs in two dimensions, each axis of collision is dealt with separately. Once the calculations are completed in each axis, the components of the solution are resolved to determine the magnitude and direction. Please watch the following presentation that will discuss the conservation of momentum when two objects collide.

Conservation of Momentum Practice

There are basically three types of problems that can be solved using conservation of momentum. First, we will solve a one dimensional problem involving a perfectly inelastic collision. Then, we will solve a one dimensional problem involving an elastic collision. Finally, we will solve a two dimensional collision problem. Please watch the following presentation of some example problems.

Conservation of Momentum Self-Assessment

Now it's your turn. Complete the following Conservation of Momentum problems to verify that you understand the difference between inelastic and elastic collisions.

  1. A bullet with a mass of mass 5g strikes a stationary 2kg block that is tied to a string that is 1.5 m long.   The collision is perfectly inelastic and the bullet block combination swings until the string makes an angle of 25o to the vertical.   What was the velocity of the bullet before it struck the block?

SOLUTION Links to an external site.

  1. A bullet of mass m and speed v0 is shot into a stationary block of mass 5m sitting on the edge of a table of height h. The bullet emerges with a speed v0 /2. How far forward does the block get before it hits the ground?

SOLUTION Links to an external site.

  1. A ball with a mass of 5.0kg and a velocity of 2 m/s at 0o collides with a 7.5kg ball with a velocity of 3m/s at 145 degrees.   After the collision the first ball is traveling 2.5 m/s at -60 degrees.   What is the velocity of the second ball after the collision?

SOLUTION Links to an external site.

Conservation of Momentum Practice Problems

Download Conservation of Momentum  Practice Problems Links to an external site. for more practice. 

Download solutions Links to an external site. to the practice problems. 

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