What is half-life?

A pulley system can lift a load of 1200 N by an effort of 250 N. If the resistance due to the weight of movable parts and friction is 300 N.Find the total number of pulleys in the system.
A) 2
B) 4
C) 6
D) 8

"Estimate the average mass density of asodium atom assuming its size to be about 2.5.(Use the known values of Avogadro's number and sodium's atomic mass.). Compare it with the density of sodium in its crystallinephase: 970 kg $m^{-<!--\; -\; -->3}$. Are the two densities of the sameorder of magnitude? If so, why?"

Atomic number refers to the number of present in an atom.
neutrons
electrons
protons

The half-life for radioactive decay of 14C is 5730 years. An archaeological artifact containing wood had only 80% of the 14C found in a living tree. Calculate the sample's age.

The half-life for the radioactive decay of C-14 is 5730 years.How long will it take for 30% of the C-14 atoms in a sample of C-14 to decay?

What is the mass number of an atom which contains 28 protons, 28 electrons, and 34 neutrons?
A) 28
B) 56
C) 62
D) 90

The first allowed excited state of a hydrogen atom is 10.2 eV above its lowest energy (ground) state. To what temperature should hydrogen gas be raised so that inelastic collisions may excite an appreciable number of atoms to their first excited state.
A. $17.88\times <!--\; \times \; -->{10}^{4}K$
B. $7.88\times <!--\; \times \; -->{10}^{4}K$
C. $157.88\times <!--\; \times \; -->{10}^{4}K$
D. $237.88\times <!--\; \times \; -->{10}^{4}K$

How does the sun burn in space as the sun is a ball of fire?

Potassium exits in mainly two isotopic form,39k and 41k and their abundance in nature are 93% and 7%. What is the average atomic mass of potassium.

The positively charged atom is known as a _______

Gram Atomic mass is just the atomic mass expressed in grams ...ie, atomic mass with gram as units. One more information about it gram atomic mass and gram atom are the same thing. Later a formula is given that: Gram atom = mass in grams / Atomic mass [RAM]. There are questions also that use this formula in which we have to find the number of "gram atoms " in a given mass of substance. So what is the real meaning of gram atom and the formula?

What are the advantages of nuclear energy?

A Atom has a nucleus which is surrounded by electrons and protons. A cell in a leaf also has a nucleus, so the nucleus in the leaf also has electrons and protons surrounding it?

${\displaystyle g(x)={\int <!--\; \int \; -->}_0^{2^x}\sin <!--\; \; -->(t^2)dt}$, g'(0)=

The quark epoch is when ________ was/were created.
Select one:
A. everything in normal atoms
B. protons and neutrons that still survive
C. all known matter
D. the rapid inflation of the cosmos
E. only dark energy

What key event took place during the atomic epoch?
Select one:
A. Atoms in the universe collected to form stars and galaxies.
B. The universe expanded and cooled enough to allow the first particles to appear.
C. The neutrinos were created.
D. The universe underwent a brief period of rapid expansion.
E. The universe expanded and cooled enough for electrons to orbit protons.