Question

Riaz takes 20 minutes to travel to his school with a speed of $3m/s$. How far is the school?
(A) $2km$
(B) $3.2km$
(C) $3.6km$
(D) $4.1km$

Answer 1

Hint: In this question, we have been given the speed of the boy, and the time he takes to reach the school. The given speed in the question is constant, so we can used the basic formula of speed to find out the required distance of the school from his home

Formula used:
$v={\displaystyle \frac{d}{t}}$, here $v$ is the speed of a particle, $d$ is the distance covered by the particle, and $t$ is the time taken to cover this distance.

Complete step by step solution:
We know that the speed is defined as the distance covered by a particle per unit time. So it is given by
$v={\displaystyle \frac{d}{t}}$ …………………..(1)
According to the question, the boy takes $20min$ to travel to his school with a speed of $3m/s$. So this means that we have
$v=3m/s$, ………………...(2)
$t=20min$
We know that $1min=60s$, so we have
$t=20\times 60s=1200s$ ………………...(3)
Substituting (2) and (3) in (1) we get
$3={\displaystyle \frac{d}{1200}}$
By cross multiplication, we get
$d=3\times 1200m$
$\Rightarrow d=3600m$
So the distance of the boy’s home to his school is equal to $3600m$.
But the options are given in kilometers. So we have to convert this distance in kilometers.
We know that $1m={\displaystyle \frac{1}{1000}}km$. So the distance is
$d={\displaystyle \frac{3600}{1000}}km$
$\Rightarrow d=3.6km$
Thus, the school is $3.6km$ far.

Hence, the correct answer is option (C).

Note: Although there is nothing directly mentioned related to the acceleration of the boy, but then also we have taken it to be zero. In the question, it is given that the boy is travelling to his school with a speed of $3m/s$. So this clearly means that his speed must be constant during his whole journey from his home to his school.