A ball is projected horizontally from an incline so as to strike a cart slinding frictionlessiy in the incline \( 6 m \) away (as shown). At the instance the ball is thrown, the speed of cart is ' \( u \) ' (in \( m / s \) ). T value of ' \( u \) ' so that the ball strikes the cart.(neglect height of cart and point of projection'of ball above the incline)