Answer:
The mass number is the product of number of protons and number of neutrons
The atomic number is the same as the mass number but just put amu next to the number
since child is moving along with the wagon and we need to find the acceleration of child inside that wagon then in this case the system of interest must be child + wagon
System of interest will be the system that is used to find the force or acceleration using Newton's law
Here we have to assume that system on which if we will calculate the forces then the net value of force on that system will help to calculate the unknown quantities
So here our system will be boy + wagon
Efficiency =Velocity Ratio/Mechanical Advantage *100%
80%=6/MA*100%
Therefore MA=7.5
MA=Load/Effort
7.5=300/E
E=300/7.5
E=40
