A ball 𝐴 is thrown up vertically with speed 𝑢 and at the same instant another ball 𝐵 is released from a height ℎ. At time 𝑡, the speed of 𝐴 relative to 𝐵 is

Question : A ball 𝐴 is thrown up vertically with speed 𝑢 and at the same instant another ball 𝐵 is released from a height ℎ. At time 𝑡, the speed of 𝐴 relative to 𝐵 is