(answered) 
the simulation kept track of the variables and automatically recorded data on object displacement, velocity, and momentum. if the trials were run on a real track with real gliders, using stopwatches and meter sticks for measurement, how might the data compare? check all that apply.
this- there would be variables that would be hard to control, leading to less reliable data
- the data would be just as valid if it were recorded with a stopwatch.
this- meter sticks may lack precision or may be read incorrectly.
this-  real glider data may vary since real collisions may involve loss of energy.
this human error in recording or plotting the data could be a factor.
- controlling real glider velocities by hand would be just as accurate as simulation controls.

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.