Let initial velocity be 𝑢 , for the minimum initial projection speed (w.r.t belt), velocity of the body at the other end should be zero w.r.t the conveyor belt, which is moving with 𝑣 velocity in opposite direction. There will be slipping, hence the retardation will be -𝜇𝑔with the total length of 𝑑
⟹𝑢2=2𝜇𝑔𝑑
⟹𝑢=𝜇𝑔𝑑