A. Initial Measurements
- Measure the length of the pendulum.
the mass of the pendulum cup in the following way: remove the pendulum arm
from the apparatus and bring it to the digital balance.
Place the blocks of wood vertically next to the scale.
Make sure the pendulum is parallel to the table with the cup on the
scale and the pendulum head on top of the wood.
- Measure the mass of the projectile.
- Set the spring tension in the gun to its maximum setting.
B. Determination of Pendulum Velocity and the Initial Velocity of the Projectile
M = combined mass of pendulum cup and ball,
L = length of pendulum, and
V = velocity after impact.
Using the conservation of energy,
- Return the pendulum to the vertical position. Make sure the angular protractor mounted
on the support is properly zeroed.
- Fire the gun five times and record the rise of the pendulum after each shot as measured
by the angle on the protractor. Remember to read the scale to 1/10 th of the smallest
- Use a spreadsheet to record the angles and to calculate the velocity after the collision
using the conservation of energy for each shot.
- The momentum, P, is defined as the product of mass and velocity, and is a quantity we
will devote a chapter to later on. The momentum of ball and holder after the collision is
Pafter = MV. The momentum before the impact is that of just the ball since only
the ball is moving: Pbefore = mballv0, where v0
is the initial velocity of the ball. The law of conservation of momentum tells us that Pafter
= Pbefore so that
v0 = MV/mball.
Calculate v0 for each shot and then calculate the average with a 90%