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Date	November 2017	Marks available	2	Reference code	17N.3.HL.TZ0.7
Level	Higher level	Paper	Paper 3	Time zone	0 - no time zone
Command term	Determine	Question number	7	Adapted from	N/A

Question

The ${\Lambda ^0}$ (Lambda) particle decays spontaneously into a proton and a negatively charged pion of rest mass 140 MeV c^–2. After the decay, the particles are moving in the same direction with a proton momentum of 630 MeV c^–1 and a pion momentum of 270 MeV c^–1.

Determine the rest mass of the ${\Lambda ^0}$ particle.

[4]

a.

Determine, using your answer to (a), the initial speed of the ${\Lambda ^0}$ particle.

[2]

b.

Markscheme

$\Lambda$ momentum = 900

E_proton = « $\sqrt {p{c^2} + {{\left( {m{c^2}} \right)}^2}} = \sqrt {{{630}^2} + {{938}^2}} =$ » 1130 «MeV»

E_pion = « $\sqrt {{{270}^2} + {{140}^2}} =$ » 304 «MeV»

so rest mass of $\Lambda$ = « $\sqrt {{{\left( {1130 + 304} \right)}^2} - {{900}^2}} =$ » 1116 «MeV c^–2»

a.

«E = $\gamma$ mc² so» $\gamma$ = « $\frac{{1434}}{{1116}}$ =» 1.28

to give 0.64c

b.

Examiners report

[N/A]

a.

[N/A]

b.

Syllabus sections

Option A: Relativity » Option A: Relativity (Additional higher level option topics) » A.4 – Relativistic mechanics (HL only)

Show 27 related questions

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16N.3.HL.TZ0.8a: Explain, in terms of a conservation law, why two photons need to be created.
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19M.3.HL.TZ1.6a:
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19N.3.HL.TZ0.5a(i):
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19N.3.HL.TZ0.5a(ii):
the speed.
17N.3.HL.TZ0.7a:
Determine the rest mass of the ${\Lambda ^0}$ particle.
19N.3.HL.TZ0.5b:
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17M.3.HL.TZ2.6:
A lambda $\Lambda$ ⁰ particle at rest decays into a proton p and a pion ${\pi ^ - }$ according to the reaction

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18M.3.HL.TZ1.6a.ii:
show that the energy of the pion is about 140 MeV.
20N.3.HL.TZ0.6b:
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19M.3.HL.TZ2.8biii:
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17M.3.HL.TZ1.5b:
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Option A: Relativity » Option A: Relativity (Additional higher level option topics)

Option A: Relativity