Collisions

Question 1

(2) State what is meant by an inelastic collision.

Answer 1

kinetic energy is not
conserved (1)
• (lost ke) appears as
heat/sound (1)
• momentum is conserved
(1)

Question 2

(2) An electron and a positron collide and annihilate each other.
Two photons are produced.
Explain why two photons must be produced, rather than just one

Answer 2

momentum (must be)
conserved (1)
• so must have positive and
negative momentum (1)

Question 3

(1) In an inelastic collision there is conservation of

Answer 3

momentum

Question 4

(1) State why momentum has the unit kg.m/s.

Answer 4

(Momentum/it)equals mass x

velocity

Question 5

(6) A= Force 1 ►(OBJECT)◄ Force 2
B= Force 1 ▼(OBJ) ►(OBJ) Force 2►
Analyse both collisions in terms of momentum and kinetic energy.

Answer 5

Diagram 1
 Moving in opposite directions before collision
 inelastic collision
 stationary after collision
 momentum zero after collision
 (therefore) total momentum must have been zero
before collision
 (therefore) cars were moving at the same speed in
opposite directions (assuming cars have equal mass)
 both cars had kinetic energy before the collision
 KE zero after collision
 KE converted into heat, sound, elastic potential
energy etc.
Diagram 2
 Elastic collision / almost elastic collision
 Momentum conserved
 Momentum transferred from first to last sphere
 KE conserved / almost conserved
 (because)last sphere reaches same height as first
sphere
 Three spheres always have zero momentum
 Small amount of energy transferred to sound/heat

Question 6

(1) The total momentum of the electron and positron before the annihilation is
zero.
State the total momentum of the gamma rays after the annihilation.

Answer 6

zero

Question 7

(2) Explain how charge is conserved in a positron-electron annihilation.

Answer 7

BEFORE
positron charge is +1, electron
charge is -1 (+e and –e)
(1)
OR
total charge is zero before
(annihilation)
(1)
AFTER
gamma rays have no charge
(1)

Question 8

(6 )Compare the design and use of particle accelerators used in international
scientific research with particle accelerators used in hospitals.

Answer 8

particle accelerators use:-
 charged particles
 magnetic fields
 high frequency alternating voltages
 collisions
 centripetal force
hospital particle accelerators
 cyclotrons
 small, size of a garage
 fast moving particle hit targets
 particles absorbed by nuclei
 produce isotopes with short half lives
 only a few people needed to work them
research particle accelerators
 cyclotrons, synchrotrons,
 Large Hadron Collider, CERN
 very large, LHC more than 2 km across
 use superconducting electromagnets
 accelerate particles to close to the speed of light
 use hundreds of research scientists
 make particles collide
 try to discover new particles (Higgs Boson)