PASCO MINI LAUNCHER ME-6825A, Инструкция по эксплуатации и руководство по экспериментам

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012-05479B Mini Launcher
23
®
Experiment 5: Conservation of Energy
EQUIPMENT NEEDED
– Mini Launcher and steel ball – Plumb bob
– Measuring tape or meter stick – White paper
– (optional) 2 Photogates and Photogate Bracket – Carbon paper
– (optional) Timing System
Purpose
The purpose of this experiment is to show that the kinetic energy of a ball shot straight up is transformed
into potential energy.
Theory
The total mechanical energy of a ball is the sum of its potential
energy (PE) and its kinetic energy (KE). In the absence of
friction, total energy is conserved. When a ball is shot straight
up, the initial PE is defined to be zero and the KE = (1/2)mv
0
2
,
where m is the mass of the ball and v
0
is the muzzle speed of
the ball. See Figure 5.1. When the ball reaches its maximum
height, h, the final KE is zero and the PE = mgh, where g is the
acceleration due to gravity. Conservation of energy gives that
the initial KE is equal to the final PE.
To calculate the kinetic energy, the initial velocity must be
determined. To calculate the initial velocity, v
0
, for a ball shot
horizontally off a table, the horizontal distance travelled by the
ball is given by x = v
0
t, where t is the time the ball is in the air.
Air friction is assumed to be negligible. See Figure 5.2.
The vertical distance the ball drops in time t is given by y = (1/
2)gt
2 .
The initial velocity of the ball can be determined by measuring
x and y. The time of flight of the ball can be found using
and then the initial velocity can be found using v
0
= x/t.
Setup
➀
Clamp the Mini Launcher near one end of a
sturdy table with the Launcher aimed away
from the table. See Figure 5.1.
➁
Point the Launcher straight up and fire a test
shot on long range. Make sure the ball does not
hit the ceiling. If it does, use the medium range
throughout this experiment or put the Launcher
closer to the floor.
➂
Adjust the angle of the Mini Launcher to zero
degrees so the ball will be launched horizon-
tally.
Figure 5.1: Conservation of Energy
Figure 5.2: Finding the Initial Velocity
x
v
0
t =
2 y
g