Date: _________
Free Fall Problems (Section 2.3)
Free fall problem
 Free fall problems are acceleration problems where we know the acceleration without
being told (more than once!)
 For all free fall problems (at the surface of the earth), a = 9.8 m/s2 [down]
Steps:
1)
2)
3)
4)
Make a chart
Use arrows next to the variables to show the direction of each vector (a, vi, vf, x)
Fill in the variables that are known
Solve for those you don’t know
Type 1: “An object is dropped…”
For these problems, initial velocity is always _____________. It’s like “starts from rest”.
1. A ball is dropped from the top of a bridge, and it takes 8 seconds to hit the water.
a) How tall is the bridge?
b) How fast is the ball going just before it hits the water?
First, put directions next to variables. If up is positive, then put in the signs as shown
below. Then also add what you know. (Remember, you need 3 variables!)
a=
vi =
Solution:
vf =
y =
t =
Note: if you choose down as positive, all the signs change, but the answer does not.
Now, try problems 1 and 2 on Free Fall Problems #1.
Physics, 3/7/2016
Type 2: “A ball is thrown up from the ground...”
In this type of problem, the initial velocity is always up. Also, the primary type of problem asks
“what is the maximum height”, which means ________________.
2. A ball is thrown up from the ground at an initial speed of 20 m/s.
a) What is the maximum height the ball reaches?
b) How long before it hits the peak?
First, assume ________ is positive
a=
Solution:
vi =
vf =
y =
t =
more notes: what if we ask when will it hit the ground again?
Now, try problems 3 and 4 on Free Fall Problems #1.
Type 3: “A ball is thrown from the roof…”
In this type of problem, you have to be careful with signs!
3. A ball is thrown from the roof at an initial velocity of 20 m/s
[up]. If it takes 6 seconds to reach the ground,
a) how high is the roof?
b) what is the velocity just before it hits the ground
Assume ______________ is+. Also, note that the ball has to get
almost to the ground, so displacement will be down (so _______________)
a=
Solution:
vi =
vf =
y =
t =
Note: if the ball had been thrown down from the roof at the same speed, vi would
have been ________________ and which answers would have been different?
Now, continue with worksheet Free Fall Problems #1.