Question

It takes one minute for a passenger standing on an escalator to reach the top. If the escalator does not move it takes him $3$ minute to walk up. How long will it take for the passenger to arrive at the top if he walks up the moving escalator?

• A. 30 s
• B. 45 s
• C. 40 s
• D. 35 s

Answer 1

Answer: (B)

Let speed of elevator be $v_e$.

$t_1=\frac{L}{v_e}$

$\Rightarrow 1\min =\frac{L}{v_e}$

Let speed of person relative to elevator be $v_P$, then

$t_2=\frac{L}{v_p}$

$\Rightarrow 3\min =\frac{L}{v_p}$

when the escalator is moving:

$t_3=\frac{L}{v_e+v_p}$

$=\frac{L}{\frac{L}{1\min }+\frac{L}{3\min }}$

$=\frac{3}{4}\min =45s$