page 07 7. Muons are created in the upper atmosphere of the Earth. The mean lifetime of these muons in their frame of reference is 2.20 µs. The muons are travelling at 0.99c relative to an observer on Earth. The observer measures the mean lifetime of these muons as A 1.56 × 10−2 s B 2.20 × 10−3 s C 1.11 × 10−4 s D 1.56 × 10−5 s E 3.10 × 10−7 s. 8. Evidence supporting the existence of dark energy comes from A estimations of the mass of galaxies B the darkness of the sky (Olbers’ paradox) C large numbers of galaxies showing redshift, rather than blueshift D the accelerating rate of expansion of the Universe E the abundance of the elements hydrogen and helium in the Universe. [Turn over