# Need help with free fall problem

1. Dec 15, 2008

### lakhani7

1. The problem statement, all variables and given/known data

maria throws an apple vertically upward from a height of 1.3 meters with an initial velocity of 2.4 m/s.
A) will the apple reach a friend in a treehouse 5.3 m above ground
B)how long will the apple be in the air before it hits the the ground

2. Relevant equations
vf^2=Vi^2+2ay

3. The attempt at a solution
A) i was able to get the answer for number one using the equation above.
0^2=2.4^2+2(-9.81*y)
-5.76=-19.62y
.3m=Y
B)i am not able to get the time however. i used vf=vi+at and i was unable to get the time.
0=2.4+9.81t
.244
if any one can recommend me an equation to use i will be grateful.

2. Dec 15, 2008

### HallsofIvy

Staff Emeritus
Try y= (1/2)at^2+ vi t.

3. Dec 15, 2008

### LowlyPion

Welcome to PF.

Here are some equations that might be useful.
https://www.physicsforums.com/showpost.php?p=905663&postcount=2

There are several ways to figure the answer to part b).

You can use the equation that relates y, Vy, and t and solve the quadratic for t.

You can also figure the time and height to get to maximum and then figure the time to fall.

V = a*t the first step is easy and you already have the height from part a).

Then all you have to do is figure the time to fall from that height and add in the first part.

4. Dec 15, 2008

### lakhani7

nope that doesnt seem to help. i used the quadratic equation with it but to no avail

5. Dec 15, 2008

### LowlyPion

Your .244 secs is really just the time to the max height. You still have to add in the downward time to fall.

x = 1.3 + .3 = 1.6 = 1/2g*t2

6. Dec 15, 2008

### lakhani7

thanks lowly pion will try