Given $A =\hat{ i }+\hat{ j }+\hat{ k }$ and $B =-\hat{ i }-\hat{ j }-\hat{ k }$, then $( A - B )$ will make angle with $A$
$0^{\circ}$
$180^{\circ}$
$90^{\circ}$
$60^{\circ}$
A river is flowing from east to west at a speed of $5\ m/min$ . A man on south bank of river, capable of swimming $10\ m/min$ in still water, wants to swim across the river in shortest time. He should swim
A boat is sent across a river with a velocity of $8\, km/hr$. If the resultant velocity of boat is $10 \,km/hr$, then velocity of the river is ........$km/hr$