- LPU MCA Semester 1
- PEA515
- Unit 6
PEA515 · Unit 6: Direction sense
Direction sense test
30 practice questions · in the ETE syllabus
Key points
- Right is clockwise, left is anticlockwise
- Distance = sqrt of squared net displacements
- Direction of the start is opposite to the end
- Morning shadows point west; evening shadows point east
Direction problems track a person's position and facing direction. Use a mental compass with North at the top, East on the right, South at the bottom and West on the left; the eight directions also include North-East, South-East, South-West and North-West.
| Turn from facing North | New facing |
|---|---|
| Right | East |
| Left | West |
| Right twice (180 degrees) | South |
A right turn is clockwise and a left turn is anticlockwise. A 45 degree turn moves between neighbouring points of the eight-point compass, and 90 degrees moves two points.
For distance problems add up the east-west and north-south displacements separately: a walk of 8 km west and 6 km south ends sqrt(8^2 + 6^2) = 10 km from the start (Pythagoras). For the direction of the end point from the start use the signs of the two displacements, and the direction of the start from the end is the opposite.
Shadow rule: after sunrise the sun is in the east, so shadows point west; before sunset the sun is in the west, so shadows point east. If a morning shadow falls to your right, you face North.
Exam trap: the final distance is not the total length walked, and the start is in the opposite direction to the end point.
Try two questions
Meera walks west for 9 km, then east for 4 km, then west for 4 km, then north for 9 km. In which direction is Meera now with respect to the starting point?
- South-East
- North-East
- South-West
- North-West
Show the answer
D. Net displacement is (-9, 9) in east and north km, so the final position lies to the North-West of the start.
Why not A: Gives the opposite direction.
Why not B: Misjudges the direction by 90 degrees.
Why not C: Misjudges the direction by 90 degrees the other way.
Karan walks east for 5 km, then east for 7 km, then east for 3 km, then west for 9 km. In which direction is Karan now with respect to the starting point?
- West
- East
- South
- North
Show the answer
B. Net displacement is (6, 0) in east and north km, so the final position lies to the East of the start.
Why not A: Gives the opposite direction.
Why not C: Misjudges the direction by 90 degrees.
Why not D: Misjudges the direction by 90 degrees the other way.