Projectile Fired Horizontally Notes

Home

Breaking a water balloon - 2000 frames/second

Motion in a Plane

I. 2-D Motion & Trajectories

What kinds of objects have 2 dimensional motion?

Objects moving
along earth's surface

Planets around sun

Pendulums

Projectiles

A) Objects moving along earth’s surface (projectiles)

1. Projectile fired horizontally

Dropped/Projected Horizontally
Rutgers U.

1. V_iy = ?

V_iy = 0

2. a_y = ?

a_y = 9.8 m/s²

3. Horizontal Velocity?

(no air friction)

Horizontal Velocity
is Constant
(no air friction)

V_ix = V_x = Constant

Horizontal Distance Traveled

d_x = V_xt

(Memorize)

4 objects thrown horizontally, same height, at various speeds.

Compare their:

V_iy?

Same

(V_iy = 0)

a_y?

Same

a_y = 10 m/s²

V_y?

Same
for all

height (d_y)?

Same
at all times

time spent
in air

same

Object is thrown horizontally, only one factor determines the time in air.

Object's initial height

Which ball remains in flight the longest?

June 1997 #64

Choice 4 - (greatest height)

B) Projectile fired horizontally - Solving Word Problems

Ex) A baseball is thrown horizontally from a grandstand 20 m above ground at speed of 10 m/s.

(a) How long will the ball remain in flight before reaching ground?

Ex) A baseball is thrown horizontally from a grandstand 20 m above ground at speed of 10 m/s.

(a) How long will the ball remain in flight before reaching ground?

Horizontal Info	Vertical Info
V_x = 10 m/s	V_iy = 0 (thrown horizontally)
	a_y = +9.8 m/s²
	d_y = 20 m
	t = ?

Step 3 - Substitute and Solve

d_y = V_iyt + ½a_yt²

20 m = 0 + ½(9.8 m/s²)t²

t = 2 seconds

(b) What is the projectile's maximum range before it hits ground?

Range?

Range (dx)

Horizontal	Vertical
V_x = 10 m/s	V_iy = 0 (thrown horizontally)
d_x = ?	a_y = +9.8 m/s²
t = 2 sec	d_y = 20 m
	t = 2 sec

Range

Horizontal Displacement (d_x)

d_x =V_xt

= (10m/s)2 secs

= 20 m

Projectile, Angle