gr 11 energy physics question?

[Red Petals]

trying to find the force of friction on an object on pavement

initial velocity is 10 m/s
finishing velocity is 0 m/s (object comes to rest)
distance it takes to come to rest is 25m
mass of object is 80 kg
initial kinetic energy is 1000J

which formula should i use?

net force= mass x acceleration
(find acceleration using v^2=V^2+ad

OR

W= Fd
(find w using second kinetic energy - initial kinetic energy)

Please tell me why which i should use and why i shouldn't use the other one.

thankyou in advance

[Jan M]

F=m*a a=v/t v=d/t
a=d/t*t
F=m*d/t*t

find t > Ek=1/2*m*(v*v) where v=s/t

Ek=1/2*m*(s/t)**

s/t=**/ 2Ek/m

s/t=5 > t=s/5
t=25/5
t=5

F=m*a
F=m*s/(t*t)
F=80*25/25

F=80N