A 8.40-g bullet is moving horizontally with a velocity of +345 m/s, where the si

Question

A 8.40-g bullet is moving horizontally with a velocity of +345 m/s, where the sign + indicates that it is moving to the right (see part a of the drawing). The bullet is approaching two blocks resting on a horizontal frictionless surface. Air resistance is negligible. The bullet passes completely through the first block (an inelastic collision) and embeds itself in the second one, as indicated in part b. Note that both blocks are moving after the collision with the bullet. The mass of the first block is 1212 g, and its velocity is +0.712 m/s after the bullet passes through it. The mass of the second block is 1538 g. (a) What is the velocity of the second block after the bullet imbeds itself? (b) Find the ratio of the total kinetic energy after the collision to that before the collision.

Explanation / Answer

There are two basic types of collisions, elastic and inelastic. Elastic is where the kinetic energy is the same before and after the collision. Inelastic is where the kinetic energy is more before the collision than it is after the collision, i.e. some of the kinetic energy is lost. Note that in both types, the momentum is ALWAYS conserved. To work out whether the collision is elastic or inelastic, you can use the equation for kinetic energy E=1/2*m*v^2 Use this equation to work out the kinetic energy before and after the collision. If it is the same, then it is an elastic collision. If it is not the same, then it is an inelastic collision.

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