Projectile Fired Horizontally

← Object Propelled Horizontally All Lessons Projectile, Angle →

Do Now: Define the geometry term “plane” and explain why a table top is an example of a plane surface.

Fill in the Blank Notes

Motion in a Plane

Plane — a 2-dimensional surface

Question

What kinds of objects have 2-dimensional motion?

Objects Moving Along the Earth’s Surface

Planets around Sun

The Copernican system of planetary rotation

Pendulums

Projectiles

Human Cannonball

at the 2007 State Fair of Texas

Human_Cannon_Ball.mov

Review

Object Projected Horizontally

Object propelled horizontally, dropped photo sequence

Question

1. V_iy = ?

↓

V_iy = 0

Question

2. a_y = ?

↓

a_y = 9.8 m/s²

Question

3. Horizontal Velocity?
(no air friction)

↓

Horizontal Velocity is Constant (no air friction)

V_ix = V_x = Constant

Horizontal Distance Traveled (Memorize)

d_x = V_xt

Compare Four Projectiles

4 objects thrown horizontally, same height, at various speeds

Compare their…

V_iy? • a_y? • V_y? • height (d_y)? • time spent in air?

↓

V_iy? — Same (V_iy = 0)

a_y? — Same (a_y = 9.8 m/s²)

V_y? — Same for all

height (d_y)? — Same at all times

Time spent in air — Same

Ranking Task

All objects below are thrown horizontally.

Rank the time each spends in the air from longest to shortest.

June 1997 #64

↓

Object is thrown horizontally — only height determines the time in air.

Ex 1

Given

A baseball is thrown horizontally from a grandstand 20 m above the ground at a speed of 10 m/s.
Find: (a) How long will the ball remain in flight before reaching the 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

Ex 1 (b)

Given

Same baseball (V_x = 10 m/s, t = 2 sec, from part (a)).
Find: What is the projectile’s maximum range before it hits the ground?

Range (d_x)

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

↓

Horizontal Displacement (d_x)

d_x = V_xt

= (10 m/s)(2 sec)

= 20 m

| Dartfish |

School blocks YouTube?

| Onsite |

Review

Question

Which velocity is constant for all spheres?

↓

V_x

AP Question

Hewitt Question

Given

A cannonball is fired horizontally at 10 m/s from a cliff. Its speed one second after being fired is about:
A. 10 m/s B. 14 m/s C. 16 m/s D. 20 m/s

↓

V_x = V_y = 10 m/s

V = 14 m/s

AP Physics

Review of Freefall

Question

Compare the time it takes for a whiffle ball to go up with the time it takes to reach its initial position.

↓

Takes longer to return from the peak — friction causes the average velocity to be less on the way down.

Ex 2

Given

A baseball is dropped from the top of bleachers at a height of 80. meters. At the same time, another ball is thrown horizontally. Both balls hit level ground 50. m apart. (Air resistance is negligible.)
Find: the horizontal velocity of the thrown ball.

↓

Time in Air

Δd_y = V_iyt + ½a_yt²

Δd_y = ½a_yt²

80 m = (4.9 m/s²)t²

t = 4 sec

V_x = d_x/t = 50 m / 4 sec

V_x = 13 m/s

Ex 3

Given

An object moving horizontally with speed V falls off the edge of a vertical cliff and lands a distance d from the base of the cliff.
Find: How far from the base of the cliff would the object land if the height of the cliff was doubled?

↓

d_x = V_xt = d

d_y = ½at²

Double d_y, then t increases by √2

(√2)d, or 1.4d

Ex 4

Given

From a cliff of height 28.8 m above the ground, a ball is thrown horizontally with an initial velocity of 7.0 m/s.
Find: What is the range of the ball?

↓

d_x = V_xt

Δd_y = ½a_yt²

28.8 m = 4.9t²

t = 2.4 sec

d_x = V_xt = (7.0 m/s)(2.4 s)

d_x = 17 m

Frame of Reference

http://www.archive.org/

Producer: Richard Leacock. Production Company: Educational Development Corp. Sponsor: Eric Prestamon. Audio/Visual: sound, black and white. PSSC

Projectile, Angle →