When solving kinematics problems, there are five variables,

v_{yo}

y

t

v_{y}

a_{y}

Notice that the "y" subscript has been added. This is additional information to indicate that these vectors are in the horizontal direction (up and down). These are 4 equations that are used,

When solving problems make y_{o} equal to zero. This means that when the description of the motion begins, that's the origin. To make it easy to compare answers, make all the displacement, velocities and accelerations that point to the up positive in the equations. Make all the variables that point down, negative.

Example #4 (Review)

A ball is tossed nearly vertically upwards at 4.0 m/s off a very tall cliff. What is the ball's position after being in the air for 3.00 seconds?

Solution

Example #5 (Review)

A ball is tossed nearly vertically upwards at 4.0 m/s off a very tall cliff. What is the ball's velocity after being in the air for 3.00 seconds?

Solution

Choose the best answer. It does not matter how many questions you miss. What matters is that you learn from any mistakes.

A rock is thrown vertically upwards at 10 m/s off the edge of a tall building. The rock passes the building and lands on the ground 15 m below its starting point. Choose all of the variables that are negative.

A rock is thrown vertically DOWNWARDS at 10 m/s off the edge of a tall building. The rock lands on the ground 15 m below its starting point. Choose all variables that are negative.

A rock is dropped off the edge of a tall building. The rock lands on the ground 15 m below its starting point. Choose all variables that are negative.

A rock is thrown vertically upwards at 10 m/s off the edge of a tall building. The rock hits a bird flying 2.0 meters overhead. The rock is moving upwards when it impacts the bird. Choose all variables that are negative.

A rock is thrown vertically upwards at 10 m/s off the edge of a tall building. The rock reaches the highest point and because of a slight horizontal breeze, lands on the roof of a taller building. Choose all variables that are negative.

x_{o}

x

v_{o}

v

a

t

What is the value of x_{o} in all of our projecitle motion problems?

zero

depends on the problem

There is one kind of problem where the displacement, x, the initial velocity, v_{o}, and the acceleration all have the same sign. Which set up is it?

choice "A"

choice "B"

choice "C"

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