CCCT9012 Our Place in the Universe
Mid-term exam
March 21, 2018
Length of exam: 75 minutes
Students are allowed to bring a piece of A4 paper, written or printed on both sides, into the
examination.
Provide explanations and steps on how you arrive at the answers. Little credit will be given
to answers without adequate explanations. Do not include information in your response
that is not related to the solution. Use diagrams to illustrate your answers as necessary. The
weighting of marks do not necessarily reflect the difficulty of the problems.
1. An HKU Lecturer routinely purchases lunch on 3rd St. in Sai Ying Pun. For most of the
year, he notices that he enjoys shelter from the midday sun provided by buildings on
this street. However, at times, these shadows no longer appear or are too short to
provide any relief. Which buildings are providing the shade, the ones on the north or
south side of the street? [10] During which season or seasons will the shade
disappear? [10]
The path of the sun is tilted towards the south so that most of the year in HK,
midday shadows should point north. This means the buildings on the north side of
the street will not cast a shadow onto the street. It will be the shadows of buildings
on the south side