PASCO ME-6815 PROJECTILE CATCHER ACCESSORY - Manual (Page 9)

012-05091E Projectile Catcher Accessory
5
Exp 1: Ballistic Pendulum
EQUIPMENT NEEDED
– Projectile Launcher (ME-6800) -meter stick
– Projectile Catcher Accessory (ME-6815) -white paper
[Velcro must be assembled (See Figure 3)] -carbon paper
– Base and Support Rod (ME-9355) -mass balance
– table clamp
Optional: Photogates and Photogate Bracket
Purpose
The muzzle velocity of the Projectile Launcher can be determined by shooting the ball into
a ballistic pendulum and then measuring the height reached by the pendulum.
Theory
A ball is launched horizontally and embeds in the bob of a pendulum. The pendulum then
swings up to a particular height, h. (See Figure 1.1.)
Momentum is conserved during the collision, but kinetic energy is not. The momentum
after the collision is equal to the momentum before the collision:
(1) m
b
v
o
= m
b
+ m
c
v
where m
b
is the mass of the ball, v
o
is the muzzle velocity of the ball, m
c
is the mass of the
catcher, and v is the velocity of the catcher (and ball) after the collision.
The kinetic energy of the catcher (and ball) after the collision is converted completely to
potential energy at the top of the swing:
(2)
1
2
m
b
+ m
c
v 2 = m
b
+ m
c
gh
CAUTION! DO NOT LOOK DOWN BARREL! CAUTION! DO NOT LOOK DOWN BARREL! CAUTION! DO NOT LOOK DOWN THE BARREL.
LONG RANGE MEDIUM RANGE SHORT RANGE
Position of Ball
Launch
SHORT RANGE PROJECTILE LAUNCHER ME-6800
Yellow Band in Window Indicates Range. 9 0 8 0 7 0 6 0 5 0 4 0 3 0 2 0 1 0 0
WEAR SAFETY GLASSES WHEN IN USE.
Use 25 mm
balls ONLY!
v
m
b
+ m
c
Launcher
CAUTION! DO NOT LOOK DOWN BARREL! CAUTION! DO NOT LOOK DOWN BARREL!
CAUTION! DO NOT LOOK DOWN THE BARREL.
LONG RANGE MEDIUM RANGE SHORT RANGE
Position of Ball
Launch
SHORT RANGE PROJECTILE LAUNCHER ME-6800
Yellow Band in Window Indicates Range. 9 0 8 0 7 0 6 0 5 0 4 0 3 0 2 0 1 0 0
WEAR SAFETY GLASSES WHEN IN USE.
Use 25 mm
balls ONLY!
v
o
m
b
m
c
Launcher
Before Collision After Collision
Figure 1.1: Conservation of Momentum