Answer:
1.86s Â
Explanation:
Given parameters:
Initial velocity  = 1.2m/s
Final velocity  = 6.3m/s
Acceleration  = 2.75m/s² Â
Unknown:
Time it takes for the child to accelerate the car  = ?
Solution:
Acceleration is the rate of change of velocity with time.
  a  = [tex]\frac{v - u}{t}[/tex] Â
a is the acceleration
v is the final velocity
u is the initial velocity
t is the time taken
        2.75  = [tex]\frac{6.3 - 1.2}{t}[/tex] Â
         5.1 = 2.75t
         t  = 1.86s Â
     Â