An astronaut tightens a bolt on a satellite in orbit. He rotates in a direction opposite to that of the bolt, and the satellite rotates in the same direction as the bolt. Explain why. If a handhold is available on the satellite, can this counter-rotation be prevented

yes it can be prevented

Explanation:

The sensation of weightlessness that astronauts experience seems to make their tasks almost effortless. However, as Newton's third law of motion suggests, working in space can be physically demanding. 

As he tightens the bolt, he is rotating in the direction opposite to the bolt

It is possible if the handhold is designed in three dimensional motion where the astronaut motion will be the uplimb motion with the mass centre of hand move along circular helix trajectory

Angular momentum is conserved astronaut motion is conserved when net external torque is Zero.

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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.