A man standing on a weighing machine in a lift records his weight in the machine as under: (i) w1 when the lift acceleration upwards at 5 m/s2 (ii) w2 when the lift acceleration downwards at 5 m/s2 (iii) w3 when the lift moves up at 5 m/s (iv) w4 when the lift moves down at 5 m/s Which of the following gives a correct relation between their relative values. (a) w1 > w2 > w3 > w4 (b) w1 = w2 > w3 > w4 (c) w1 w3 = w4 < w1

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.

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