Masalah saat Memukul bola menggunakan kekuatan di Corona SDK

Saya sedang mengembangkan permainan seperti Hoki Udara. Saya ingin Memukul bola dengan kekuatan untuk itu saya menggunakan kode berikut, tetapi masalah dengan kode ini adalah terkadang saat memukul (menabrak) palu dengan keping, palu tersebut menghilang dan setelah itu terkadang keping juga menghilang dari layar, saya tidak dapat mengetahui apa masalah sebenarnya dari hilangnya objek dari layar, tetapi jika saya mengubah local start = self.points[1] menjadi local start = self.points[2] di getVelocity berfungsi kemudian skenario menghilang yang sama terjadi, Silakan coba selesaikan masalah sejak lama saya terjebak dalam masalah ini, saya baru mengenal Corona.Terima kasih.....

local sqrt = math.sqrt
local physics = require("physics")
physics.start()
physics.setGravity(0,0)
physics.setDrawMode("debug")


local source
local target

-- Track velocity
local velocityTracker = {
    points = {}    
}

function velocityTracker:reset()
    self.points = {}
end

function velocityTracker:addPoint(time, x, y)   
    -- Only keep 10 points
    local count = #self.points + 1
    if count == 11 then
        count = 10
        for i=1,10 do
            -- Move older points to top
            self.points[i] = self.points[i+1]
        end 
    end
    self.points[count] = {time = time, x = x, y = y}
end

function velocityTracker:getVelocity(moves)
    if #self.points < 2 then
        return 0
    end

    local start = self.points[1]
    local totalVelocity = 0
    local now = system.getTimer()
    for i=2,#self.points do
        local finish = self.points[i]
        -- Use a vector to determine velocity
        local timePassed = finish.time - start.time
        local age = now - finish.time
        -- Only use recent points
        if age < 200 then
            local vector = {x = finish.x - start.x, y = finish.y - start.y}
            local distance = sqrt(vector.x^2 + vector.y^2)
            -- Calculate velocity
            totalVelocity = totalVelocity + (distance / timePassed)
        end
        start = finish
    end
    return totalVelocity
end

local function onPuckCollision( event )    
    if event.phase == "began" and event.other.isBall then
        -- Puck just hit a ball        
        local ball = event.other
        local puck = event.target

        -- Use a vector to determine direction of hit
        local vector = {x = ball.x - puck.x, y = ball.y - puck.y}
        -- normalize vector
        local magnitude = sqrt(vector.x^2 + vector.y^2)
        if magnitude > 0 then
            vector.x = vector.x / magnitude
            vector.y = vector.y / magnitude
        end        

        -- Use velocity to determine force
        local force = 10 * velocityTracker:getVelocity()

        local function smack()
            ball:applyForce(vector.x * force, vector.y * force, ball.x, ball.y)
        end

        -- We can't modify phyiscs in a collision handler so we
        -- `performWithDelay` to cause it to execute after this function
        timer.performWithDelay(0, smack)
    end
end

local function movePuck( event )
    local t = event.target
    local phase = event.phase
    if "began" == phase then
        local parent = t.parent
        display.getCurrentStage():setFocus( t )
        t.isFocus = true
        -- Store initial position
        t.x0 = event.x - t.x
        t.y0 = event.y - t.y
        -- Save velocity tracking state
        velocityTracker:reset()
        velocityTracker:addPoint(event.time, event.x, event.y)
    elseif t.isFocus then
        if "moved" == phase then
            t.x = event.x - t.x0
            t.y = event.y - t.y0

            -- Track a movement
            velocityTracker:addPoint(event.time, event.x, event.y)
        elseif "ended" == phase or "cancelled" == phase then
            display.getCurrentStage():setFocus( nil )
            t.isFocus = false
            velocityTracker:reset()
        end
    end
    return true
end


target = display.newCircle( 250, 250, 60 )
target.x = display.contentCenterX
target.y = display.contentCenterY
target:setFillColor(240, 200, 0)
target.isBall = true
-- Don't allow sleeping because a moving static body
-- won't always wake it if it's asleep
target.isSleepingAllowed = false 
physics.addBody(target,"dynamic",{radius = target.width / 2})


source = display.newCircle( 250, 250, 60 )
source.x = display.contentCenterX
source.y = display.contentHeight - 100
source:setFillColor( 240,125,0 )
source.isPuck = true
-- Use static body if you're going to move the object instead of
-- letting the physics engine move it
physics.addBody(source,"static", {radius = source.width / 2})

source:addEventListener("collision", onPuckCollision)

source:addEventListener("touch", movePuck)

local bounds = {
    left = -target.width,
    top = -target.height,
    right = display.contentWidth + target.width,
    bottom = display.contentHeight + target.height,
}

-- Reset ball position if it leaves screen
local function resetBall()
    if target.x < bounds.left or target.x > bounds.right or
        target.y < bounds.top or target.y > bounds.bottom
        then
        target.bodyType = 'static' -- Stop current movement
        target.x = display.contentCenterX
        target.y = display.contentCenterY                
        target.bodyType = 'dynamic' -- Make movable again

        source.x = display.contentCenterX
        source.y = display.contentHeight - 100        

        display.getCurrentStage():setFocus( nil )
    end
end

timer.performWithDelay(500, resetBall, 0)