1. what is meant by half-life?

the time for a radioactive sample to reduce to half of its radioactivity.
the time for half of a radioactive sample to decay into new substances.
the time for a radioactive sample to reduce to half of its original mass.
the time for half of a radioactive sample to lose its radioactivity.

4. the isotope uranium-232 has a half-life of 68.9 years. how long will it take for 60% (n/n0 = 0.60) of the original sample to decay?

5.8 years
50.8 years
93.5 years
407 years

5. the isotope barium-133 has a half-life of 10.51 years. of a 10 kg sample, how much will remain after 50 years?

0.37kg
4.53kg
8.64kg
270kg
6. a piece of bone from a horse found in an archaeological site is dated using carbon-14 dating. it is found that the bone has 78% of the carbon-14 that it would have when the horse was alive. approximately how long ago did the horse die?

900 years ago
2,000 years ago
14,100 years ago
35,800 years ago
7. at an physics research facility 0.0027 kg of a new isotope is made in an atomic collider. after 6 seconds, 0.00147 kg remain. what is the half-life of the isotope?

0.25 seconds
5.26 seconds
6.84 seconds
500 seconds

What is the function of the commutator in a dc motor? a. to spin the magnet b. to change direct current into alternating current c. to change alternating current into direct current d. to spin the wire coil

In which of the following cases is work being done on an object? question 2 options: pushing against a locked door carrying a box down a corridor pulling a trailer up a hill suspending a heavy weight with a strong

Fill in the blanks with the numbers is a measure of the resistance to flow. a high liquid has a high resistance to flow and flows slowly. the ancients thought everything in the world was made of 4 we now know that there are 94 naturally occurring and scientists have created another 24 i am certain they will create even more. honey flows slowly because it has a high to flowing. a can be separated by physical means because it contains more than one pure substance and 2 pure substances are not chemically bonded to each other. a cannot be separated by physical means. all matter is made up of all elements are with the same number of protons. if it is just a single or many bonded together, if all of them have the same number of protons, it is an element. in a piece of pure iron metal, all the are joined together, that piece of iron metal is called elemental iron. a single of iron is called elemental iron. a mixture has differences from place to place. we might need a microscope to see them or they might be obvious to the unaided eye. there are surfaces separating it into different phases. a mixture is the same everywhere. it is uniform. there are no surfaces separating it into different phases. if different kinds of atoms (different elements) are bonded together by their electrons, it is called a there are physical means of to isolate the different pure substances in a mixture and there are chemical means of to isolate the different elements in a compound. 1. element 2. compound 3. mixture 4. heterogeneous 5. homogeneous 6. pure substance 7. atoms 8. separation 9. viscosity 10. resistance