Suppose two snooker balls each having a momentum collide with each other
and then rebound.
Before collision
After collision
B
A
A
The momentum of A and B
added together before the
collision.
Before U1
2 m/s
M1=2kg
U2
The momentum of A and B
added together after the
collision.
=
1 m/s
M2=1kg
B
After
V1
1 m/s
M1=2kg
V2
3m/s
M2=1kg
Total momentum before the collision = Total momentum after the collision
Momentum of M1 + Momentum of M2 = Momentum of M1 + Momentum of M2
Describe what has happened to the momentum during the collision.
Another way of writing this is in equation form as follows:
(M1 x U1) + (M2 x U2) = (M1 x V1) + (M2 x V2)
1. Two trolleys collide in the following way:
U1
5 m/s
M1=100kg
U2
0 m/s
M2=200kg
V1
1 m/s
M1=100kg
V2
? m/s
M2=200kg
(a) Calculate the value of V2 after the two trolleys collide.
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(b) Write down a formula for Kinetic Energy.
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(c) Calculate the kinetic energy of both trolleys before and after the collision
and decide if it was an elastic or inelastic collision.
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2. Suppose the same two trolleys were to collide again but they somehow stick
together and move off with a common velocity.
U1
5 m/s
M1=100kg
U2
0 m/s
M2=200kg
V
M1=100kg
M2=200kg
Calculate the common velocity V.
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3. Both trolleys are initially travelling towards each when they collide.
U1
M1=4kg
1 m/s
U2
1 m/s
M2=3kg
V1
0.5 m/s
M1=4kg
V2 ? m/s
M2=3kg
(a) During the collision M1 rebounds with a velocity of 0.5 m/s. Find V2.
(HINT: When placing the values of the velocities into the equation the direction of the velocity must
also be considered!)
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(b) Examine the kinetic energy of the trolleys before and after the collision and
then comment on the result.
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(4) A bullet of mass 45 g is travelling horizontally at
400 m/s when it strikes a wooden block of mass 16
kg suspended on a string so that it can swing freely.
The bullet is embedded in the block.
Calculate the velocity of the combined block and
bullet after the collision.
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Recoil Velocity
600 m/s
(5) A rifle of mass 3 kg fires a
bullet with a mass of 20 grams
with a velocity of 600 m/s.
(a) Name the type of collision involved in this situation.
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(b) Discuss whether both energy and momentum are both conserved during
this type of collision.
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(c) Calculate the recoil velocity of the rifle.
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A=1kg
A=1kg
B=2kg
B=2kg
4. Two trolleys are pushed together against a spring and
held at rest. The trolleys are then released and the spring
causes them to “explode” apart.
(a) If trolley A is given a velocity of 2 m/s to the left,
find the velocity of B.
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(b) If the spring takes 2 second to expand and drop away from the trolleys calculate:
(i) the change of momentum per second of trolley A. ______________________ (1)
(ii) the change of momentum per second of trolley B. ______________________ (1)
(iii) Do both the trolleys receive the same force during the collision? Challenging
question here: There are two ways in which you could deduce the answer can you think
of both?
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(iv) If the spring took a longer time to expand back to its original shape do you think the
force on the trolleys would be the same? ___________________________________ (1)
(v) Explain. _________________________________________________________ (1)
5. (a) Why are seat belts designed to stretch during
a collision? ________________________________
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(b) What is the purpose of an air bag? ___________
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(c) Why does a cricket batsman, a tennis player, a footballer or a golfer “follow
through” when hitting the ball? ____________________________________________
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1.
2.
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(ii) Momentum of the rocket.
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(ii) Velocity of the rocket.
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3.