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Physics Homepage Resource Book Online "Textbook" Syllabus

AP Physics 2 Homepage Resource Book Online "Textbook" Syllabus

Solving Vertical Projectile Motion Problems

To succeed, the student must first memorize the kinematics formulae.

To use these formulae correctly, the right signs must be applied and these rules obeyed.

1. Xo = 0 at the beginning of the motion.
2. Xo is loactaed at the beginning of the projectile motion.
3. Vo ALWAYS points in the positive direction. If Vo is zero, then assume the acceleration points in the positive direction.

Rules for Signs   Displacement The vector for displacement starts at Xo. When the displacement vector points in the same direction as Vo, "x" is positive in the formulae. Otherwise it is negative. Velocity When the velocity vector points in the same direction as Vo, "V" is positive in the formulae. Otherwise it is negative. Acceleration When the acceleration vector points in the same direction as Vo, "a" is positive in the formulae. Otherwise it is negative. When solving problems, select two locations. These two locations will the where the final and initial positions and velocities come from. The time, "t" variable, will measured between these two locations. One of the locations should be the location to answer the question.   Click here to see an animation illustrating how the signs change with the projectile's motion.

...How high did the arrow travel? (The top of the motion.)

...How fast was the bullet traveling when it left the gun barrel? (At the gun barrel)

...How fast was the swimmer traveling when she landed in the water? (At the water.)

The other location should be either determined by other parts of the question or a location that you inherently know a lot about ...like apogee.

Example:

...How long was the Arrow in the air? (The point where the arrow was launched and the point where is landed)

...How high did the bullet travel from the ground? (Use the the ground as one location of variables and the highest point as the other location.)

The motion can also be broken up into sections. The following may help with identifying variables.

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

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