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This text is meant to accompany class discussions. It is not everything there is to know about energy. It is meant as a prep for class. More detailed notes and examples are given in the class notes, presentations, and demonstrations (click here.)

Click here for questions that go along with this section on Impulse and momentum.

Impulse from a Graph

This equation works because the force is constant. If the force changes over time, a graph will be used to determine the impulse instead of the product of "Ft."

If the force that changes the momentum of an object is applied over time then a graph can be plotted to calculate the impulse.

This method provides one more way to calculate the impulse. Impulse can be calculated by the formulas, J=m(change-in-v) and J=Ft and the areas between the curve and axis.

Example 1

Question
Hint
Solution

A 250 kg motorcycle and rider is moving at 15 m/s when she slows down by applying the force according to the diagram above. What is the motorcyclist's final velocity after applying this force for 15 seconds?

HINT:

The motorcyclist is moving with an initial momentum, (mv,) before the impulse removes some of that momentum. This is described as Impulse=(mass)(change-in-momentum). The impulse is the area between the "curve" and the axis from 0 to 15 seconds.

A 250 kg motorcycle and rider is moving at 15 m/s when she slows down by applying the force according to the diagram above. What is the motorcyclist's final velocity after applying this force for 15 seconds?

HINT:

The motorcyclist is moving with an initial momentum, (mv,) before the impulse removes some of that momentum. This is described as Impulse=(mass)(change-in-momentum). The impulse is the area between the "curve" and the axis from 0 to 15 seconds.

Solution:

Question
Solution

A 1400 kg car accelerate in in first gear following the force vs time graph shown below. If the car starts from rest, What is its final speed after 2 seconds?

by Tony Wayne ...(If you are a teacher, please feel free to use these resources in your teaching.)

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