Atoms begin to gravitate together to form a center
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
Answer:

Explanation:
Given that,
Initial velocity of an object, u = 22 m/s
Final velocity of an object, v = 36 m/s
Time, t = 5 s
It can be assumed to find the average acceleration of the object instead of average velocity.
The change in velocity per unit time is equal to average acceleration of an object. It can be given by :

So, the acceleration of the object is
.
Answer:
6.0 N
Explanation:
The strength of a force is expressed as the magnitude of the force in Newton.
The formula to apply here is :
Force= mass * acceleration
F=ma
Mass, m = 4 kg
Acceleration = 1.5 m/s²
Force= 4 *1.5 = 6.0 N
Weight equals mass times gravitational acceleration=400N, so mass=400/9.8=41kg approx.