Question

Two bullets are fired horizontally and simultaneously towards each other from roof tops of two buildings 100 m apart and of same height of 200m with the same velocity of 25 m/s. When and where will the two bullets collides. (g =10 m/s$^2$)

• A. after 2s at a height 180 m
• B. after 2s at a height of 20 m
• C. after 4s at a height of 120 m
• D. they will not collide

Answer 1

Answer: (A)

after 2s at a height 180 m

Answer 2

$t = \frac{d}{v_{rel}} = \frac{100}{50} = 2\,s$
$s_y = - \frac{1}{2} gt^2$
$= -\frac{1}{2} \times 10\times 4 = -20$
$\therefore$ Height = 180 m
Therefore, the correct option is (A) : after 2s at a height 180 m