If a 20 kg box is accelerating upward at 8 m/s^2 , what is the magnitude of the upward force

356 N

Explanation:

Newton's second law of motion describes the relationship between an object's mass and the amount of force needed to accelerate it.  

here there is a weight acting downwards on the object , yet it is accelerating  upwards shows that there is a net force upwards

Applying Newtons second law of motion upwards ,

Force  = mass *acceleration

Upward force - m*g = m *a

F_up= 20 *8 + 20 * 9.8

         = 356 N

Upward force= 160 N

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.