Transcript Regents Physics

Physics Lab
– Thursday 12/16/04
– Pick-up materials on front desks
– Intro to Horizontal Motion Lab
– Bring physics HW to do in class
 Agenda
Physics
 Agenda Thursday 12/16/04
– Return Plane Labs
– Horizontal Motion
– HW: Read p. 155-157 and probs. p. 170 #8, 9, 22
Projectile Motion
A projectile can be anything that moves
though the air after it has been given an
initial “thrust” or input force
 Projectiles are only under one force as they
move through the air –GRAVITY!
 We ignore air resistance in most cases to
simply the problems
 There are two general categories

– Projectiles launched horizontally
– Projectiles launched at an angle
Projectile Motion

Bullet Demonstration
 Ballistics Cart Demo
Important Concepts
1. Vertical and horizontal motions are
independent of each other
2. We can relate the height, time in the air, and
initial vertical velocity of the projectile by
using its vertical motion, then determine the
range (x-distance)
3. We use basic motion equations to solve!
What do You Notice??
Projectiles Launched Horizontally
A cat is tossed horizontally at 20 m/s
off a cliff that is 50 m high.
a) How long is the cat in the air?
b) How far from the base of the cliff
does the cat land?
c) How fast is the cat moving the
Instant before it splats on the ground?
Problems Solving Strategy
1. Write known and unknown variables
 2. Write variables for x and y directions

What’s missing?
vyf = ?
yi = 0
vyi = 0
vxi = 20 m/s
ay = g = -9.8m/s2
ax = 0
WHY?
vxf = 20 m/s
vnetf = ?
yf = -50 m
xi = 0
t=?
xf = ?
Practice Problem #2

A plane that is moving 200 m/s drops a
package. The package takes 15 seconds to
reach the ground.
– A) What height was the package dropped from?
– B) How far did the plane travel from the time the
package was released until the package hit the
ground? Is this the same distance the package
travels?
– C) How fast was the package moving when it hit the
ground?
End
Regents Physics
Agenda –
 Projectile Motion:

– Projectiles at any angle

HW: problems p. 160 #12,13
problems p. 172 #42, 47 (tricky)
Review Problem

A plane that is moving 225 m/s drops a
package. The package takes 10 seconds to
reach the ground.
– A) What height was the package dropped from?
– B) What horizontal distance did the package cover
after it was dropped from the plane?
– C) How fast was the package moving when it hit the
ground?
Projectiles at Any Angle..a few
differences

When projectiles are launched at any angle,
the initial velocity has both horizontal and
vertical components

This means that
Vxi
… we’ve
Vxi = Vocos 
Vyi = Vosin 
Vo must be used, not just
done this before!
Variables of Motion
Other differences and similarities

Time in air is called flight time and ½ of
flight time occurs at ½ range
 So..it takes the same amount of time to go
up as it does to fall down
 At ymax, Vyf = 0m/s
 Still, only force acting on the is gravity
 Still, no acceleration in the x direction!
Practice Problem
A football is thrown with an initial velocity of 5.5 m/s
at an angle of 49 above the horizontal.
1. How long did it take the ball to return to the
launching height?
2. What was the maximum height the ball attained?
3. What was its range?
Vyf = 0 m/s
Max height
range
Let’s Play Golf
Regents Physics
 Agenda
 Review
HW Problems and Lab
 Circular Motion
 HW: Read p. 163-168

Problems p. 166 #14-16
Circular Motion

Question: Can an object be accelerated if
its speed remains constant?

What’s uniform circular motion?
It is the movement of an object or point mass
at constant speed around a circle with a fixed
radius
Circular Motion

Demo