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The diagram shows the gamma rays produced when positrons and electrons collide and annihilate - Edexcel - GCSE Physics - Question 5 - 2015 - Paper 1

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The diagram shows the gamma rays produced when positrons and electrons collide and annihilate. (i) The total momentum of the electron and positron before the annihi... show full transcript

Worked Solution & Example Answer:The diagram shows the gamma rays produced when positrons and electrons collide and annihilate - Edexcel - GCSE Physics - Question 5 - 2015 - Paper 1

Step 1

(i) State the total momentum of the gamma rays after the annihilation.

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Answer

The total momentum of the gamma rays after the annihilation is also zero. This is due to the conservation of momentum, where the total momentum before the collision must equal the total momentum after.

Step 2

(ii) Calculate the total mass of the positron and electron before annihilation.

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Answer

To find the total mass, we can use the equation derived from Einstein's mass-energy equivalence, where the total energy is given by:

E=mc2E = mc^2

We rearrange this to solve for mass:

m=Ec2m = \frac{E}{c^2}

Substituting the given values:

m=1.6×10−13 J(3.0×108 m/s)2m = \frac{1.6 × 10^{-13} \, J}{(3.0 × 10^8 \, m/s)^2}

Calculating:

m=1.6×10−139.0×1016≈1.77×10−30 kgm = \frac{1.6 × 10^{-13}}{9.0 × 10^{16}} ≈ 1.77 × 10^{-30} \, kg

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