Projectile Motion

Projectile motion is the movement of an object

 that is propelled vertically, with only the force of gravity acting on it.

EQUATION: s1 = -16t² + vit +s2

Assuming that there is no air resistance, this equation can be used to find problems

with "free fall" and "vertical launch."

To use this equation, you must understand it first.

-16t² represents the force of gravity in mathematical terms (feet/sec²)

vi represents the initial velocity of the object

t represents time

s represents the objects position in feet above the ground

(both initially and finally)

Now you should try it in a problem:

A throwing machine propels a ball upward with and initial velocity of 55 feet/sec.

How many seconds after the ball is propelled is it 42 ft above the ground?

Solution: Use the equation s1 = -16t² + vit +s2 ,

where vi = 55 ft/sec and s2 = 0 ft.

The equation then looks like s1 = 16t² - 55t.

Write the equation -16t² + 55t = 42 in standard form

16t² - 55t + 42 = 0

and use it in the quadratic formula:

so, your answer would be t = 2.292… or t = 1.145…

meaning that the ball reaches 42 feet in about 1.15 seconds on the way up,

and again at about 2.29 seconds (on it’s way back down).

Good luck on the quiz…..