Answer:
magnitude of the average acceleration is 4.16 m/s²
Step-by-step explanation:
given data 
initial velocity u = 5 m/s
distance s = 3 m 
final velocity v = 0
to find out 
magnitude of the average acceleration
solution
we will apply here linear motion equation that is 
v²-u² = 2×a×s ..............1
put here all these value 
v is final velocity and u is initial velocity and s is distance 
0²-5² = 2×a×3
a = -4.16
so magnitude of the average acceleration is 4.16 m/s²