Energy = Power x Time
Energy = 20W x 10s
Energy = 200 joules
As they are Alkali metals (group 1), they are extremely reactive in both air and water so must be stored in kerosine to stop them from reacting with the air or water.
Answer:
The bubble gum experiment demonstrates the law of conservation of mass in that even though the bubble gum has lost mass, this loss in mass is not because some matter present in the gum has been destroyed, but it has changed form and has been removed from the gum.
Explanation:
In this science experiment, students investigate whether or not chewing gum should be considered eating. During the process of chewing the gum, the gum loses mass. The experiment is used to demonstrate the law of conservation of mass which states that matter can neither be created nor destroyed but may change from one form to another.
The loss in mass of the gum is due to the fact that the sugar present in the gum has changed form and has been removed from the gum. During the process of chewing the gum, the sugar in solid form present in the gum is dissolved in the saliva found in the mouth. The dissolved sugar is then swallowed and passes into the digestive tract for digestion. This shows that even though the bubble gum has lost mass, this loss in mass is not because some matter present in the gum has been destroyed, but it has changed form and has been removed from the gum, This demonstrates the law of conservation of mass.
The weight of the meterstick is:

and this weight is applied at the center of mass of the meterstick, so at x=0.50 m, therefore at a distance

from the pivot.
The torque generated by the weight of the meterstick around the pivot is:

To keep the system in equilibrium, the mass of 0.50 kg must generate an equal torque with opposite direction of rotation, so it must be located at a distance d2 somewhere between x=0 and x=0.40 m. The magnitude of the torque should be the same, 0.20 Nm, and so we have:

from which we find the value of d2:

So, the mass should be put at x=-0.04 m from the pivot, therefore at the x=36 cm mark.
They both Move energy through a Field without Moving A Substance