Question

Boy F stays 5 km from school. For the first 4 km he takes a taxi, which drives at a speed of 60 km/hour. Thereafter, the boy walks at a constant pace of 50 m per minute. Show, in a sketch or a diagram, how long it takes him to get to the school

Answer 1

Let $s=$ distance in meters, $v=$ velocity in meters per minute, $t=$ time in minutes.

The equation of the uniform line motion

$$s=vt$$

Solve for $t$

$$t={s\over v}$$

Given for boy F

$$s_1=4 \ km=4000\ m,$$

$$v_1=60\ km/h=\dfrac{60000\ m}{60\ min}=1000\ m/min$$ $$s_2=5\ km-4 \ km=1000\ m,$$

$$v_2=50\ m/min$$

Then

$$t_1=\dfrac{4000\ m}{1000\ m/min}=4 \min$$

$$t_2=\dfrac{1000\ m}{50\ m/min}=20 \min$$

$$t=t_1+t_2=4\ min+20\ min=24\ min$$

A boy F takes 24 minutes to walk from home to school.