**PROBLEM SOLVING TACTICS** **Force And Motion**

Tactic 1: Dimensions and Vectors Many students fail to grasp the second Key Idea in , arid that failure haunts them through the rest of this book. When you are dealing with forces, you cannot just add or subtract their magnitudes to find their net force unless they happen to be directed along the same axis.

Tactic 2: Reading Force Problems Read the problem statement several times until you have a good mental picture of what the situation is, what data are given, and what is requested. If you know what the problem is about but don’t know what to do next, put the problem aside and reread the text.

Tactic 3: Draw Two Types of Figures You may need two figures. One is a rough sketch of the actual situation. When you draw the forces, place the tail of each force vector either on the boundary of or within the body on which that force acts. The other figure is a free body diagram: the forces on a single body are drawn, with the body represented by a dot or a sketch. Place the tail of each force vector on the dot or sketch.

Tactic 4: What Is Your System? If you are using Newton’s second law, you must know what body or system you are applying it to. In Sample Problem 5- I it is the puck (not the ice). It is the cookie tin. In it is the tire (not the people).

Tactic 5: Choose Your Axes Wisely In Sample Problem 5-3, we saved a lot of work by choosing one of our coordinate axes to coincide with one of the forces (the y axis with F).

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