Difficulty: Easy
Correct Answer: 9 cm East
Explanation:
Introduction / Context:
This direction sense question describes an insect walking along straight segments with right turns and a specific absolute movement towards the North. We must find the insect's final position relative to its starting point in terms of East–West displacement. The trick is to interpret the sequence of right turns correctly and track horizontal and vertical displacements separately, then compare the final coordinate with the origin.
Given Data / Assumptions:
Concept / Approach:
We will track the insect's path on a coordinate grid where East–West displacements affect the x-coordinate and North–South displacements affect the y-coordinate. Some segments may cancel the vertical displacement (such as equal South and North movements), leaving only horizontal displacement. At the end, we compare the final coordinates to the origin to see whether the insect is East or West of the starting point and by how much in centimetres.
Step-by-Step Solution:
Step 1: Assume the starting point is (0, 0).
Step 2: Walking 15 cm East takes the insect to (15, 0); it is facing East.
Step 3: From facing East, a right turn faces South. Walking 20 cm South leads to (15, -20).
Step 4: From facing South, a right turn faces West. Walking 4 cm West takes it to (11, -20).
Step 5: The insect then turns towards North (absolute direction) and walks 20 cm, moving to (11, 0). The Southward and Northward movements cancel.
Step 6: From facing North, a left turn faces West. Walking 2 cm West moves the insect to (9, 0).
Step 7: The final position is (9, 0) compared to the starting point (0, 0), so the insect is 9 cm to the East of its starting point.
Verification / Alternative check:
We can sum the horizontal and vertical movements separately. Horizontally, the insect moves 15 cm East, 4 cm West, and 2 cm West. Net horizontal displacement = 15 − 4 − 2 = 9 cm East. Vertically, it moves 20 cm South and 20 cm North, which cancel to zero. Therefore, the insect ends up directly East of the starting point by 9 cm. This matches the coordinate approach and confirms that there is no North–South displacement in the final position.
Why Other Options Are Wrong:
21 cm East or West ignores the net cancellations and overestimates the displacement. 9 cm West would only occur if the Westward movements exceeded the Eastward movement, which is not the case here. 4 cm North assumes there is a net vertical displacement, but the 20 cm South and 20 cm North movements cancel exactly, leaving no net North–South shift. Hence only 9 cm East is consistent with the described path.
Common Pitfalls:
Students may misinterpret the change from relative directions (right/left) to absolute directions (North) and then back to relative directions (left from North), leading to incorrect final directions. Another common error is to add distances without considering direction or to forget to subtract movements in opposite directions. Drawing a simple diagram, marking each turn, and writing cumulative East–West and North–South components is a robust strategy to avoid such mistakes.
Final Answer:
The insect is now located 9 cm East of its starting point.
Discussion & Comments