Question

Two particles are projected from a tower horizontally in opposite directions with velocities 10 m//s and 20 m//s. Find the time when their velocity vectors are mutually perpendicular. Take g=10m//s^2.

Answer 1

the time at which their velocity vectors are mutually perpendicular are t=1.4sec

Given the horizontal velocities are u1=10i

                                                                                  u2=-20i

                      vertical velocities are given by at u=0 ;a=g

                                                   v1=v2=-10tj

                        the velocity vectors are given by particle1=10i-10tj

                                                                                  particle 2=-20i-10tj

two velocities are mutually perpenicular if their dot product is zero

        (10i-10tj).(-20i-10tj)=0

    ⇒t=1.4 sec