There is a 30 g sample of Be-11. It has a half-life of about 14 seconds. How much will be left after 28 seconds?A.3.75 gB.7.5 gC.15 gD.30 g

After 28 sec 7.5 grams of Be will be left

Explanation:

Given data:

Total amount of Be = 30 g

Half life of Be = 14 sec

Mass left after 28 sec = ?

Solution:

First of all we will calculate the number of half lives in 28 sec.

Number of half lives = T elapsed / half life

Number of half lives = 28 sec / 14 sec

Number of half lives = 2

AT time zero = 30 g

At first half life = 30 g/2 = 15 g

At second half life = 15 g/ 2 = 7.5 g

So after 28 sec 7.5 grams of Be will be left.

question: ray weighs 100 kilograms, his wrestling partner, bobby, weighs 50 kilograms. if ray moves at 4 m s , how fast will bobby have to run at him to apply an equal amount of kinetic energy?

answer: 8 m/s he needs to run twice as fast to keep up so he has some work to do

explanation:   if the mass has units of kilograms and the velocity of meters per second, the kinetic energy has units of kilograms-meters squared per second squared.

question answered by

(jacemorris04)

the best answer is d because the strong cohesion is caused by the ability of water molecules to undergo hydrogen bonding.

a is incorrect because when water solidifies, it becomes   ice, which expands and occupies a bigger volume for the same mass of water in its liquid state.

b is incorrect because water has high surface tension. besides bonding to itself it hydrogen bonds to other molecules at the top decreasing possibility for breaking of attractive forces.

c is incorrect because the water molecule has oxygen which is highly electronegative and so pulls the electron pair towards itself creating a dipole moment, making the molecule polar.

e is incorrect because water has strong adhesion, ability to stick to other molecules such as glass because of this molecules having stronger hydrogen bonding than water.