Question

A man is standing between two parallel cliffs and fires a gun. If he hears the echoes after 1.5s and 3.5s respectively, the distance between the cliffs is (velocity of sound in air = 340m/s)

• A. 1190m
• B. 850m
• C. 595m
• D. 510m

Answer 1

The correct option is B 850m

Suppose d is the total distance between two cliffs and x is the distance between the man and one cliff.
$2x=v\times t_1$

$x=\frac{v\times t_1}{2}$

$=\frac{340\times 1.5}{2}$

$=255m$

$2(d-x)=v\times t_2$

$(d-x)=\frac{v\times t_2}{2}$

$(d-x)=\frac{v\times t_2}{2}$

$(d-x)=\frac{340\times 3.5}{2}$

$(d-x)=595m$

$d=595+x$

$=595+255$

$=850m$