The friction force is 1.5N
Now, using the third equation of motion-
[tex]v^{2}= u^{2} +2as[/tex]
v=final velocity
u=initial velocity
a=acceleration
s=distance
substitute the values in the above equation
1.2=0+ 2a×20
a=1.2/40
a=0.03
friction force=mass ×acceleration
=50×0.03
=1.5N
hence, The friction force is 1.5N
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