d. Maintain constant velocity
Explanation:
A constant velocity leads to no acceleration. 
Acceleration is defined as the change in velocity with time: 
   Acceleration = 
If there is no change in velocity i.e constant velocity. 
At constant velocity, the change in velocity is 0. 
  If we put zero in the equation above, we will obtain an acceleration value of 0. 
Learn more: 
Acceleration brainly.com/question/3820012
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There are 3 bases before you reach home plate.
        
             
        
        
        
For an uniformly accelerated motion, we can write

where 

 is the acceleration of this motion, which in this problem is the gravitational acceleration, with a negative sign because it points downward, against the direction of the motion; h=0.540 m is the distance covered by the flea, and 

 is the initial velocity. 
At the maximum height, the velocity is zero, so 

. Therefore we  can solve to find 

:
 
 
        
        
        
Answer:
P.E = 0.068 J = 68 mJ
Explanation:
First we need to find the height attained by the ball toy. For this purpose, we will be using 3rd equation of motion:
2gh = Vf² - Vi²
where,
g = -9.8 m/s²  (negative sign due to upward motion)
h = height attained by the ball toy = ?
Vf = Final Velocity = 0 m/s (since it momentarily stops at the highest point)
Vi = Initial Velocity = 3 m/s
Therefore,
2(-9.8 m/s²)h = (0 m/s)² - (3 m/s)²
h = (9 m²/s²)/(19.6 m/s²)
h = 0.46 m
Now, the gravitational potential energy of ball at its peak is given by the following formula:
P.E = mgh
P.E = (0.015 kg)(9.8 m/s²)(0.46 m)
<u>P.E = 0.068 J = 68 mJ</u>