What is missing from this free body diagram of a sled being pulled across level ice by a dog team
the normal force
the force that the dogs exert on the ground because of the weight
the velocity vector arrow for the sled
the reaction force that the ground exerts on the dogs to push them forward

The normal force

Explanation:

There are four forces acgint on the sled:

- the driving force, exerted by the dogs which pull the sled forward

- the frictional force, that act in the opposite direction of the driving force (backward)

- the weight of the sled, which is directed downward

- the normal force, which is the reaction of the surface on which the sled slides, and which pulls opposite to the weight (upward)

From the graph, we see that the only missing force is the one which is directed upward, so it must be the normal force.

i think its

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.