From the graph
Initial velocity u = 20 m/s
Final velocity v = 0m/s
t = 10 s
m = 20
g = 20/100 kg
F = ma
= \(m\frac{(\text{v}-\text{u})}{t}\)
= \(\frac{20}{1000}\times\frac{(0-20)}{10}\)
= -0.04 N
The negative sign shows that the frictional force is acting opposite to the direction of motion of the object.
