6) A boat crosses a river at a constant engine speed of 2.0 m/s under pointed Directly west. The river runs directly south at 2.5 m/s. If the river is 126 meters wide, how long does it take the boat to cross the river? 7) If the pilot of the boat doesn't correct for the current, how far downstream will he land on the opposite shore?

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.

the answer is the index of refraction of the second medium is higher. i just took the test.