Two particles 1 and 2 are thrown in the directions shown in figure simultaneously with velocities `5 m//s and 20 m//s.` Initially, particle 1 is at height 20 m from the ground. Taking upwards as the positive direction, find

(a) acceleration of 1 with respect to 2
(b) initial velocity of with respect to 1
(c) velocity of 1 with respect to 2 after time `t= 1/2 s`
(d) time when the particles will collide.

Answer

A, B, C, D

Explanation

(a) `a_1=a_2=-g`
`:. a_(12)=a_1-a_2=0`
(b) `u_(21)=u_2-u_1=20-(-s)`
`=+25 m//s`
(c) `u_(12)=-u_(21)=-25 m//s`
Since, `a_(12)=0`
`:. u_(12)`=constant
`=-25 m//s`
(d) `a_(12)=0.` Therefore, relative motion between
them is uniform with constant velocity `25 m//s.`
`:. t=d/v=20/25=0.8s`