A person climbs up a stalled escalator in $60 \mathrm{~s}$. If standing on the same but escalator running…
A person climbs up a stalled escalator in $60 \mathrm{~s}$. If standing on the same but escalator running with constant velocity he takes $40 \mathrm{~s}$. How much time is taken by the person to walk up the moving escalator?
$37 \mathrm{~s}$
$27 \mathrm{~s}$
$24 \mathrm{~s}$
$45 \mathrm{~s}$
Solution
Person's speed walking only is $\frac{1}{60} \frac{\text { "escalator" }}{\text { second }}$
Standing the escalator without walking the
speed is $\frac{1}{40} \frac{\text { "escalator" }}{\text { second }}$
Walking with the escalator going, the speed add.
So, the person's speed is $\frac{1}{60}+\frac{1}{40}=\frac{15}{120}$
$\frac{\text { "escalator" }}{\text { second }}$
So, the time to go up the escalator ("seconds per escalator") is
$
t=\frac{120}{5}=24 \text { second }
$