A student needs to move a large carton of books with a total mass of 120 kg, to get a better view out the window. The coefficient of static friction (μs) between the cardboard boxes and the tile floor is 0.42, and the coefficient of kinetic friction (μk) is 0.30. With what horizontal force will the student have to push in order to get the stack of books to start moving? Round to the nearest whole number and include units.

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.

conservation of mass

mass before something happens = mass afterwards