Radium–226 decays by alpha emission to radon–222, which in turn decays by alpha emission to polonium–218. The half-life of Radium–226 is 1620 years while the halflife of radon–222 is 3.83 days. (a). What is the equilibrium ratio of the number of Radium–226 nuclei? (b) How much time was initially required to establish that equilibrium?

air exerts forces on falling objects near earth’s surface.

explanation:

the term 'free falls' refer to object that are falling towards the earth, in a situation in which gravity is the only force acting on the object.

for an object in free fall, the acceleration is constant (g, the gravitational acceleration), and so the velocity of the object constantly increases.

for objects near earth's surface, there is always another force acting on the object: the resistance due to the air. this force is opposed to the direction of fall of the object, and it is proportional to the velocity of the object, so as the object falls down, this force increases up to a point when it balances the force of gravity, and the object continues its motion at constant velocity (called terminal velocity). since in this case gravity is not the only force acting on the object, we are not in a situation of free fall.

54 degrees incident angle = reflected angle

angle is from normal turned to line of ray

the best answer for these questions would be:

1.            c. is smaller

2.            d) concrete operational

3.            b) interaction with the environment – the children interact with their environment can them learn more.

4.            a) parents who reason openly with children can limit a child’s cognitive ability.