Question

20 kg object travels 28 meter and stops. coefficient friction= 0.085 how much work was done by friction?

Answer 1

Assuming it is on a horizontal surface:
friction = μR
R = 20g (g is gravity 9.81)
so Friction = 0.085 x 20g
Work done is force x distance 
so Work done = 0.085 x 20g x 28
 = 466.956 J