Corona sdk: Small Lua coding issue

Corona sdk: Small Lua coding issue

I was watching this Corona tutorial
The code that I want to ask about is this
mine1 = display.newImage("mine.png")
mine1.x = 500
mine1.y = 100
mine1.speed = math.random(2,6)
mine1.initY = mine1.y
mine1.amp = math.random(20,100)
mine1.angle = math.random(1,360)
physics.addBody(mine1, "static", {density=.1, bounce=0.1, friction=.2,
radius=12})
screenGroup:insert(mine1)
mine2 = display.newImage("mine.png")
mine2.x = 500
mine2.y = 100
mine2.speed = math.random(2,6)
mine2.initY = mine2.y
mine2.amp = math.random(20,100)
mine2.angle = math.random(1,360)
physics.addBody(mine2, "static", {density=.1, bounce=0.1, friction=.2,
radius=12})
screenGroup:insert(mine2)
mine3 = display.newImage("mine.png")
mine3.x = 500
mine3.y = 100
mine3.speed = math.random(2,6)
mine3.initY = mine3.y
mine3.amp = math.random(20,100)
mine3.angle = math.random(1,360)
physics.addBody(mine3, "static", {density=.1, bounce=0.1, friction=.2,
radius=12})
screenGroup:insert(mine3)
Now when the plan goes up, it blows, i don't want it to blow no matter how
high it goes, i just want to to blow if it hits a mine, how to do so?