Download Conservation of Momentum AIM To determine the momentum of a

Conservation of Momentum
AIM To determine the momentum of a system before and after an interaction, and to compare
these two quantities.
Momentum of an object is defined as the product of its mass and velocity.
momentum = mass x velocity
The symbol for momentum is (logically!?) 'p'. We can therefore write the above definition
in symbolic form as
p = mv
Since the units for m are ........, and the units for v are ........., it is logical that the units for p
must be ...........
Note also that since velocity is a vector and mass is a scalar, that momentum must also be
a vector with the same direction as the velocity.
Do not confuse INERTIA with MOMENTUM. The inertia of an object is a measure of its
resistance to a change in velocity and is related only to the mass of the object. It is possible
therefore for an object to have a large inertia and a small (even zero!) momentum or vice
versa.
Set out the answers to the following questions carefully. Write (a) the relevant equation in
symbolic form (b) substitute without calculation (c) complete the calculation and (d)
include the units in the answer
1. What is the momentum of a 60 kg person running at 10 m s—1?
2. How fast would a 1000 kg car travel to have the same momentum?
3. What is the momentum of a 20 g bullet travelling at 500 m s—1?
4. A 360 g trolley moving at 2.4 m s—1 collides and coalesces with a 200 g trolley
travelling in the opposite direction at 1.8 m s–1. What is the resultant velocity of the
trolleys?
AIM
To determine the momentum of a system before and after an interaction, and
to compare these two quantities.
METHOD
Set up the following apparatus. The spring-loaded propulsion device on the
left hand trolley in the diagram is compressed and the trolleys are separated
"explosively" by pressing the release device on this trolley. Note that the
recording ticker tapes cross the opposite trolley in order to record the motion
of each trolley as they are propelled away from each other.
In this experiment, both trolleys are initially stationary and they are accelerated by the
release of the spring-loaded propulsion device on one of the trolleys. The ticker timers
provide a record of the motion of the after the interaction.
The masses of the two trolleys should be measured and recorded.
Trolley A ___________
Trolley B ___________
ANALYSIS Use the paper tape to find the speeds of the trolleys after the interaction.
Since the trolleys are initially accelerating as the spring pushes them apart,
do not use this section of the tape. You will have to decide how much of the
tape to use to get a velocity value that is reliable. Discuss in your report the
two conflicting factors that must be taken into account in calculating the
velocities.
From this information and the measured masses of the two trolleys, find the
momentum after the "explosion. Compare the sum of these values with the
total initial momentum and comment on this result in terms of the law of
conservation of momentum (you should state this law).
1. Using Newton's second law, F = ma and the definition of acceleration, determine an
alternative expression for this law in terms of momentum.
2. Define the term IMPULSE and state the two equivalent units used for this quantity
3. At what minimum speed must a golf ball leave the club if it is to travel 200 metres
before it lands? (assume 45° initial angle). What momentum change occurs while the
club is in contact with the ball? (you will need to find the mass of a golf ball!). What do
you think the average force acting on the ball is during this contact time? Be prepared
to discuss your answer with the class when this report is handed in.
AIM
To determine the momentum of a system before and after a collision and
compare these two quantities.
METHOD
Set up the following apparatus.
In this experiment, the first trolley with mass m1 is initially stationary and is then
accelerated by the mass hanging on the string. When it reaches the trolley m 2 it collides
and the two trolleys will continue in the same direction. The ticker timer provides us with
a record of the motion of the trolley before and after the collision. The masses of the two
trolleys should be measured and recorded.
ANALYSIS Use the paper tape to find the speed of the trolley prior to the collision and
the speed of the two trolleys after the collision. Since the trolleys are
accelerating in both cases, you will have to decide how much of the tape to
use to get a value that is reliable. Discuss in your report how there are two
conflicting factors which make this difficult.
From this information and the measured masses of the two trolleys, find the
momentum just prior to the collision and just after the collision. Compare
these values and comment on them in terms of the law of conservation of
momentum (you should state this law).
Q4. Using Newton's second law, F = ma and the definition of acceleration, determine an
alternative expression for this law in terms of momentum.
Q5. Define the term IMPULSE. What are the SI units for impulse?
Q6. At what minimum speed must a golf ball leave the club if it is to travel 200 metres
before it lands? (assume 45° initial angle). What momentum change occurs while the
club is in contact with the ball? (you will need to find the mass of a golf ball!). What
do you think the average force acting on the ball is during this contact time? Be
prepared to discuss your answer with the class when this report is handed in.