Humans sleep in cycles, usually two or three cycles per night. there is a point in each cycle when waking up will leave the sleeper feeling the most rested and refreshed. after learning about this, a computer programmer designed a new smartphone alarm clock. this new alarm clock uses sensors in the smartphone to detect the sleeper’s motion and determine when the sleeper has reached the best point in the sleep cycle at which to wake up. the app can be downloaded onto any smartphone. most users who download this app find that it does not them wake up feeling more refreshed, but they are willing to try improved products in the future. which criterion did this sleep cycle alarm clock fail to meet? it did not solve the problem. it was not cost effective enough. it was not readily available. it was not safe for most users.

it did not solve the problem

It did not solve the problem.

Explanation: Basically, if people download a sleep cycle alarm clock app to wake up feeling more refreshed but it does not happen, the problem is not solved.

For the rest of the options we need to know more information that is not available in the text. For example, the cost of the app.

answer: the correct answer is 1.

explanation: there are various process in which a radioactive nuclei decays:

1) alpha decay: in this process, a heavier nuclei decays into lighter nuclei by releasing alpha particle. the mass number is reduced by 4 units.

2) electron capture: in this decay process, a parent nuclei absorbs an electron and gets converted into a neutron. simply, a proton and an electron combines together to form a neutron. mass number does not change in this process.

3) gamma ray emission: it is a decay process in which an unstable nuclei gives excess energy by a spontaneous electromagnetic process. this decay releases . this process does not change the mass number.

4) positron emission: it is a type of decay process, in which a proton gets converted to neutron and an electron neutrino. this is also known as -decay. in this the mass number remains same.

from the above information, we see that only alpha-decay is producing a change in the mass number of the nucleus.

trig 15.3 cos