Linear Momentum (College Board AP® Physics 1: Algebra-Based): Study Guide

A tennis ball of mass 60 g and a brick of mass 3 kg are both launched in the same direction. The tennis ball acquires a velocity of 75 m/s and the brick acquires a velocity of 1.5 m/s. Compare the inertia and momentum of the tennis ball and the brick.

Answer:

Step 1: Determine the momentum of the tennis ball

Step 2: Determine the momentum of the brick

Step 3: Compare the momentum of each object

• Both the tennis ball and the brick have the same momentum

• Therefore, it is equally difficult to change the velocity of both objects

Step 4: Compare the inertia of each object

• The brick has more mass, therefore, it has greater inertia than the tennis ball

• Therefore, it is harder to change the acceleration of the brick

  • Consider this: which would you rather hit with a tennis racket, the tennis ball, or the brick?

Momentum problems quickly become complex when dealing with systems of interacting objects (e.g. collisions), and issues often stem from a misunderstanding of the vector nature of momentum. When analyzing a scenario, read the question carefully to see if positive and negative values have already been assigned. If not, the initial direction of motion is usually assigned the positive direction.