PASCO ME-6829 Mini Launcher Ballistic Pendulum - Manual (Page 15)

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M o d e l N o . M E - 6 8 2 9 E xp e r i m e n t 3 : C o n s e r v a ti o n o f M o m e n tu m a n d E n e r g y
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9. Calculate the torque (
τ) applied to the pulley by the string.
τ = R
pulley
F
T
10. Calculate the rotation inertia (I) of the pendulum-ball sys-
tem using the rotational form of Newton’s 2nd Law:
τ = Iα
I = _____________________
Analysis
1. Calculate the initial angular momentum of the ball
(L
launch
) just before the collision. The angular momentum
is calculated about the pendulum pivot.
L
launch
= m
ball
Vlaunch
2. Calculate the angular momentum of the ball-pendulum
system (L
0
) immediately after the collision.
L
0
= I
ω
0
3. Calculate the kinetic energy of the ball (K
launch
) before the
collision.
4. Calculate the kinetic energy of the ball-pendulum system
(K
0
) immediately after the collision.
5. Use the maximum angular displacement of the pendulum
(
θ
max
) to calculate the change in height (h
max
) of the ball.
Refer to Figure 3.5.
6. Calculate the gain in potential energy of the ball (
∆U
ball
).
∆U
ball
= m
ball
g h
max
Questions
1. Why did you calculate the ball’s rotational momentum
rather than the linear momentum? Why did you calculate
the rotational momentum around the pendulum pivot rather
than the center of the ball?
2. Compare the rotational momentum of the ball before the
collision to the rotational momentum of the pendulum-ball
system just after the collision. Was momentum conserved?
Figure 3.5: Calculating h
q < 90°
h
q < 90°
h
Center of ball
K
launch
1
2
---m
ballV0
2
=
K
0
1
2
---I ω
0
2
=