An indicator of average kinetic energy is temperature. Temperature is directly proportional to Kinetic energy of the molecules of an element.
Radioactive "decay" means particles and stuff shoot OUT of a nucleus.
After that happens, there's less stuff in the nucleus than there was before.
So the new mass number is always less than the original mass number.
The net force on an object subject to friction is equal to the sum of the applied force and the frictional force.
Mathematically,

Here, m is mass of object and a is its acceleration. We take frictional force negative because it opposes the motion of object.
Given,
,
and 
Substituting these values in above formula, we get
.
Thus, the acceleration of an object is 