Question

From a suitable height two projectiles are thrown simultaneously horizontally in opposite direction with equal speed 20m/s then the displacement between the projectile when they are moving perpendicular to each other

Answer 1

Let a projectile is thrown along x-axis and other is thrown along negative x-axis.

Let after time t , velocity of both projectiles perpendicular to each other.

so, velocity of first projectile , v = 20i - gt j = 20i - 10t j

velocity of second projectile, v' = -20i - 10t j

velocities are perpendicular to each other. so, v.v' = (20i - 10t j).(-20i - 10t j) = 0

or, -400 + 100t = 0

or, t = 4 sec

as horizontal component of velocity remains constant so, total displacement = displacement covered by first particle during 4sec + displacement covered by 2nd particle during 4 sec

= 20 × 4 + 20 × 4

= 160m

hence, answer is 160m