An aeroplane is flying with speed 60 m/s at angle 30o with the horizontal. A shell is fired horizontally from the aeroplane. Find the direction and magnitude of velocity of theshell so that it falls vertically along a straight line with respect to the observer on the ground.

Component of velocity of aeroplane in vertical and horizontal directions are shown in the figure.For the shell to fall along a straight line with respect to the observer on the ground , horizontal component of velocity of shell with respect to ground  must be zero.For this shell must be fired horizontal opposite direction with speed of aeroplane in horizontalvB=303m/shorizontally opposite to motion of plane.