Explosions - Law Enforcement - Directions


How it Works:

Using the Explosions - Law Enforcement Concept Builder is quite simple. There are three different difficulty levels. Difficulty levels differ only in terms of the number of question presented to students. As you progress through any of the difficulty levels, you will be presented with a queston that you will have to answer. The question presents three situations involving an explosive-like impulse between two unequal-mass carts on a track. A Before-Explosion and an After-Explosion representation of the mass and velocity of each is presented. You will have to determine which of the three situtations violate the law of conservation of momentum. Tap on any situation which does. Once you tap on one or more situations, they will be displayed behind bars (since they break the law of momentum conservation) and a Check Answer button appears. Once you are satisfied with your answer, tap on the Check Answer button. Your answer will be evaluated and your Progress Report will be updated. 

The diagrams show a cart that may or may not be loaded with bricks. Each brick has the same mass as a cart. And so a cart with a brick on it has twice the mass as an unloaded cart. And a cart loaded with two bricks has three times the mass as an unloaded cart.

The diagrams also show velocity vectors for the two carts in the After Explosion diagram. The length of the arrow is proportional to the velocity. The arrow lengths are either 1-unit long, 2-units long, or 3-units long. 

By making careful observations of the mass and velocity information, and by using a momentum formula, you will be able to determine if the After Explosion momentum is the same as or different than the Before Explosion momentum.

Your goal is to earn "Stars" and to complete one or more difficulty levels. Stars are earned when you demonstrate success with a particular question. Once you show success on all the Question Groups at a particular difficulty level, you will earn the reward for that difficulty level.

Earning Stars

There are three activities in this Concept Builder. When you start up any of these activities, the number of questions for that activity are shown in the Progress Report area of the Concept Builder. You will notice that there is either a Yellow or a Red background for each question number. When starting up an activity, the background color is Yellow. Answering a "Yellow" question correctly earns you a star for that question number. However, answering it incorrectly turns the background color to Red. A question number with a Red background must be correctly answered twice (without a miss) in order to earn a star. 


Getting Help

You will notice that there is a Help Me button underneath the Progress Report. You should learn to use this feature of the program. It's how you can turn an exercise in answering questions into an exercise in learning. Tapping on the Help Me button will open a page with help that explains a detailed approach to each question. Of course, the Help pages are only helpful if you read them. So take the time to read them. Each Help page contains four sections: a discussion of the The Basic Idea, a display of the Question that you are trying to answer, a section titled "How to Think About This Situation", and a set of links to resources in our Tutorial section. You should pay attention to the section titled How to Think About This Situation. You will find what you need to know in the paragraphs of this section. You will also become a better Physics student for doing that. That is, after all, the goal of such an activity as Explosions - Law Enforcement.

Thanks for being patient with the Directions. Happy learning!




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