Name:_________________
Physics 11
UNIT 6 Motion in Two Dimension
Date:______________
6.1 – Projectile Motion Horizontally Launched
The study of projectile motion brings together a lot of what you have learned so far
 You need to know about gravity, velocity, acceleration, and vector components to
be able to fully understand (and figure out) these questions.
 Don’t worry, though. Even with all that stuff to keep track of, learning how to do
these questions and understand what is happening a little bit at a time makes it all
manageable.
A few years ago some researchers in the U.S. went to elementary schools, junior and
senior high schools, and universities and asked them to look at the following:
"Ignoring air resistance, which of the following correctly shows what an object
would do if it rolled off a cliff?"
If we look at the horizontal and vertical components of an objects velocity as it rolls off
a cliff, we would get something that looks like this.
 The x-component is there from the start, and stays the same the entire time.
 The y-component doesn’t even exist at the beginning, but grows bigger as the
object falls.
The shape of the path that it follows is actually a parabola. If you’ve studied those in
math class, great! Don't worry about it if you haven't, just as long as you recognize the
shape and know the name.
Objects launched like golf balls, basketballs, someone jumping off a cliff … etc are
_________________.
The path they follow is called a __________________.
Projectiles follow a _____________ ___________ !
When an object is thrown off a cliff it has a _____________ and a ______________ component
of motion. These 2 components are independent of each other. One does not affect the other.
http://phet.colorado.edu/sims/projectile-motion/projectile-motion_en.html
If we fire a gun and drop a bullet at the same time, the 2 bullets will hit the ground at the
_________ time.
Recall our formulas from Ch. 3 and Ch. 4. These can be applied to projectile motion.
* Objects launched horizontally – We’ll first look at the motion of objects that have an
initial vertical velocity of zero.
Example: A stone is thrown horizontally at 15
from the top of a cliff 44 m high.
(a) How long will the stone take to reach the bottom of the cliff?
(b) How far from the base of the cliff does the stone strike the ground?
(c) What are the horizontal and vertical components of the velocity of the stone just before it hits
the ground?
Horizontal Projectiles Assignment #1
Answer the following, showing all steps. Check your sig figs, hand in your assignment after you finish
1. An object is thrown horizontally at 20.0 m/s from the top of a 50.0 tall building. (a) How long until it
hits the ground? (b) What is the range of the projectile?
3.19s, 63.9 m
2. An object is launched horizontally at 10.0 m/s from the top of a 90.0 m tall building. What is the range
of the projectile?
42.8 m
3. A projectile is launched from a 1.50 x 102 m high cliff at 25 m/s. (a) How long is the projectile in the
air for? (b) What is the range of the projectile?
5.53 s, 138m
4. An projectile is launched horizontally from a cliff with a velocity of 18.0 m/s. If the projectile lands
100.0 m from the base of the cliff, how high is the cliff?
151 m
5. An object is launched horizontally from the top of a building with a velocity of 20.0 m/s. If it hits the
ground 48.0 m from the base of the building, how high is the building?
6. An object is launched horizontally from the top of a cliff with a velocity of 15.0 m/s. If it takes 5.50 s to
reach the ground, (a) how high is the building? (b) What is the range of the projectile?
(148 m high, 82.5 m)
7. A projectile is launched horizontally from the top of a cliff at a velocity of 20.0 m/s. If the object takes
4.20 s to reach ground level, (a) how far from the base of the cliff did the object strike the ground?
(b) How high is the cliff?
84.0 m, 86.4 m high
8. A projectile is launched horizontally from an 85.0 m tall building. If the projectile has a range of 67.8
m, what was the initial horizontal velocity of the object?
(16.3 m/s)
9. An object is launched horizontally from the top of a cliff with a velocity of 20.0 m/s. (a) If the object
takes 3.20 s to reach the ground, what is the range of the object? (b) What is the vertical velocity of
the object just before it hits the ground? (c) What is the total velocity of the object just before it hits
the ground (add the vertical and horizontal components)?
(a) 64.0 m, (b) 31.4 m/s (c) 37.2 m/s @57.5° below the horizontal
10.
An object is launched horizontally from a 45.6 m high cliff. If the initial velocity is 75.0 m/s, (a)
What is the time of flight? (b) What is the range of the projectile? (c) What is the vertical component
of the velocity after 1.20 seconds? (d) What is the vertical component of the velocity just before
impact? (e) What is the final velocity just before impact?
(a) 3.05 s, (b) 229 m (c) -11.8 m/s (d) -29.9 m/s (e) 80.7 m/s @21.7° below the horizontal.