# Mechanics: Momentum and Collisions

## Momentum and Collisions: Audio Guided Solution

#### Problem 20:

A Roller Derby exhibition recently came to town. They packed the gym for two consecutive weekend nights at South's field house. On Saturday evening, the 68-kg Anna Mosity was moving at 17 m/s when she collided with 76-kg Sandra Day O'Klobber who was moving forward at 12 m/s and directly in Anna's path. Anna jumped onto Sandra's back and the two continued moving together at the same speed. Determine their speed immediately after the collision.

## Habits of an Effective Problem Solver

• Read the problem carefully and develop a mental picture of the physical situation. If necessary, sketch a simple diagram of the physical situation to help you visualize it.
• Identify the known and unknown quantities in an organized manner. Equate given values to the symbols used to represent the corresponding quantity - e.g., m = 1.50 kg, vi = 2.68 m/s,  F = 4.98 N, t = 0.133 s, vf = ???.
• Use physics formulas and conceptual reasoning to plot a strategy for solving for the unknown quantity.
• Identify the appropriate formula(s) to use.
• Perform substitutions and algebraic manipulations in order to solve for the unknown quantity.

Get more information on the topic of Momentum and Collisions at The Physics Classroom Tutorial.