This question involves the concepts of Newton's Second Law of Motion and the equations of motion.
The wagon will pick up a speed of "4.5 m/s" after Heather has pushed the wagon for 3 s.
Applying Newton's Second Law of Motion to this situation:
[tex]F=ma\\\\a=\frac{F}{m}[/tex]
where,
a = acceleration = ?
F = Force applied = 72 N
m = combined mass of car and boy = 48 kg
Therefore,
[tex]a=\frac{72\ N}{48\ kg}[/tex]
a = 1.5 m/s²
Now, we will use the first equation of motion to find out the final speed of the wagon:
[tex]v_f=v_i+at[/tex]
where,
vf = final speed = ?
vi = initial speed = 0 m/s
t = time taken = 3 s
Therefore,
vf = 0 m/s +(1.5 m/s²)(3 s)
vf = 4.5 m/s
Learn more about Newton's Second Law of Motion here:
brainly.com/question/13447525?referrer=searchResults
The attached picture shows Newton's Second Law of Motion.
