Question

From a high rise tower, two balls are thrown
horizontally in opposite directions with velocities 5m/
s and 3m/s. The time after which their velocities will
be perpendicular is
(2) 5 s
(3) VISS
(4) 10 s​

Answer 1

Answer:

√0.15 seconds.

Explanation:

From the equation of motion we get that v=u-gt when the balls are dropping the acceleration is taken as -g which is 10 m/s^2. Here, in the vector form it can be written as v vector = ui -(10t)j. Since, the two balls at that point will be horizontally in opposite direction so one of the velocity will be opposite to the other,

So, for the two balls we will have -5i - (10t)j and 3i-(10t)j and for the two balls to have perpendicular we know that the dot product of the two vector will be zero. Hence,  [-5i - (10t)j].[3i-(10t)j]=0 which will be -15 +100t^2 =0 or t^2=15/100 which on solving we will get t=√0.15 seconds.