Apiece of wood from a nearby construction site floats near the shore of a lake. it floats in very calm water with half of its volume just above the surface. what is the density of this piece of wood? the density of water is 1000 kg/m3 . 1. 2000 kg/m3 2. more information is needed. 3. 500 kg/m3 4. 4000 kg/m3 5. 125 kg/m3

3. 500 kg/m3

Explanation:

The only external forces acting upon the piece of wood, are the gravity (which we call weight) and  the buoyant force due to the water removed by the wood to be partially submerged.

Both forces oppose each other, due to the gravity is always downward, and the buoyant force is always upwards.

In order to be in equilibrium, both forces must be equal in magnitude, so we can write the following:

Fg = Fb  

If the wood has only half of his volume just above the Surface, this means that the buoyant force is equal to the weight of this volumen in water, as follows:

Fb = δh2o. V/2. g

This value must be equal to the weight of the full volumen of wood:

Fg = = δw . V. g  

So, in order to Fg = Fb, it must be δw = δh2o / 2 = 500 Kg/m3

a.metals can become magnetic if they have many spinning electrons that create magnetic fields.d.only some metals are attracted by magnets; these metals are called ferromagnetic.

d.wrapping an insulated wire around a metal with ferromagnetic properties and applying an electric current.

see earlier