While an airplane is in flight, four forces act on it. thrust is caused by the airplane's propellers pushing through the surrounding air, pulling the airplane forward. drag is caused by the air smacking into the plane's surface, pushing it backward. lift is caused by the air rushing over the wings, pushing it upward. and weight is caused by gravity pulling the plane downward. which force acts on the plane at a distance?

Among these 4 forces, the only force acting on the plane at a distance is weight.

In fact, weight is due to gravity, which is a non-contact force (it acts also from a distance). All the other forces, instead, are due to the contact between the plane (or parts of it) with the surrounding air: without the air, all the other 3 forces (thrust, lift, drag) would not be present, while weight would be always present.

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.