Data Analysis
Momentum
A class studied the speed and momentum of a 0.25-kilogram ball dropped from a bridge. The graph shows the momentum of the ball from the time it was dropped until the time it hit the river flowing below the bridge.
Applying Concepts At what time did the ball have zero momentum? Describe this point in the ball's motion.
Using Graphs At what time did the ball have the greatest momentum? What was the peak momentum value?
Calculating What is the ball's speed after 1.25 seconds? (Hint: Use the graph and the momentum formula.)
Three different closed systems are shown in Figure 17. Each system consists of two train cars with the same mass that collide. In Figures 17A and 17B, the train cars collide and then bounce apart. In Figure 17C, the cars collide and then join together. Examine the momentum of each train car before and after the collision. Note that the total momentum before and after each collision does not change. The momentum is conserved.
Section 12.3 Assessment
Reviewing Concepts
Using Newton's third law, explain what is meant by action and reaction pairs of forces.- State in your own words the formula for momentum.
- What is a necessary condition for the conservation of momentum?
If an eagle and a bumblebee are traveling at 8 km/hr, which has more momentum? Explain.
Critical Thinking
Applying Concepts A friend tells you that a rowboat is propelled forward by the force of its oars against the water. First, explain whether the statement is correct, and then identify the action and reaction forces.
Inferring Explain how Newton's third law of motion is at work when you walk.
Applying Concepts Explain in terms of Newton's third law why someone who tries to jump from a canoe to a riverbank may fall into the water.
Writing in Science
Explanatory Paragraph Write a paragraph explaining why it is impossible to identify a single isolated force. State in your first sentence the main idea of Newton's third law of motion.
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