Velocity of part not changing?

How the script is supposed to work: When the player presses q a part is spawned outside of their Torso/rootpart. Basically I want the parts velocity to change so it can fly upwards then downwards. The part only flys downwards and I dont know why

local fireball = game.ServerStorage:WaitForChild("Fireball")

game.ReplicatedStorage.Fireball.OnServerEvent:Connect(function(player,cframe)
    local character = player.Character
    local newFireball = fireball:Clone()
    newFireball.CFrame = character.HumanoidRootPart.CFrame

    local jump = Instance.new("BodyVelocity")
    jump.Velocity = Vector3.new(0,20,0)
    wait(2)
    jump.Velocity = Vector3.new(0,-999,0)

    jump.Parent = newFireball

    newFireball.Parent = workspace

    local touchconn

    touchconn = newFireball.Touched:Connect(function(hit)
        if hit.Parent:FindFirstChild("Humanoid") then
            if hit.Parent.Name ~= player.Name then
                hit.Parent.Humanoid:TakeDamage(0.7)
                wait(0.6)
                if touchconn ~= nil then touchconn:Disconnect() end
                newFireball:Destroy()
            end
        end
    end)
    wait(15)
    if touchconn ~= nil then touchconn:Disconnect() end
    newFireball:Destroy()
end)