SIR PLZ CLEAR MY DOUBT FOR THIS QUESTION I HAVE ASKED THIS QUESTION ALREADY BUT THE ANSWER GIVEN TO ME WAS NOT HELP FULL . A particle was projected with initial velocity 20m/s at 60 degree to horizontal. After what time its velocity will be perpendicular to initial direction of motion . CHAPTER NAME - VECTOR Share with your friends Share 0 Rajnish Kumar answered this Dear student strategy : first write the initial velocity in vector form u→ : then write the final velcity after time t when particle makes makes angle 900 with u→ let v→ :last make dot product of u→. v→=0 which gives you t as below u→=20cos600i^+20sin600j^=10i^+103j^v→=u→+a→t=10i^+103j^+10t(-j)=10i^+(103-10t)j^(10i^+103j^).{10i^+(103-10t)j^}=0100+300=1003tt=43 secRegards 0 View Full Answer