Exercise 4.2
A student runs from the ground floor to the fourth floor of a school building to collect a book and then comes down to their classroom on the second floor. If the height of each floor is m, find: (i) the total vertical distance travelled, and (ii) their displacement from the starting point.
NCERT’s answer
(i)
$\displaystyle 18$ m (ii) $\displaystyle 6$ m in upward direction
(i) Total vertical distance travelled \(\displaystyle = 18\ \text{m} \).
Going up, ground floor to fourth floor is $\displaystyle 4$ floors: \(\displaystyle 4 \times 3\ \text{m} = 12\ \text{m} \).
Coming down, fourth floor to second floor is $\displaystyle 2$ floors: \(\displaystyle 2 \times 3\ \text{m} = 6\ \text{m} \).
\(\displaystyle \text{total distance} = 12\ \text{m} + 6\ \text{m} = 18\ \text{m} \)
(ii) Displacement \(\displaystyle = 6\ \text{m} \), in the upward direction.
The student starts on the ground floor and ends on the second floor, a net rise of \(\displaystyle 2 \times 3\ \text{m} = 6\ \text{m} \); the trip up to the fourth floor and back does not add to it.