Can the work by kinetic firctionon an object be positive? Zero?

Work done by kinetic friction can be

The work done by kinetic friction on a body :

What is the kinetic energy of an object ?

Work done by a force on an object is zero, if

Can work done by a non - conservative force be positive ?

Assertion :- Work done is positive when force acts in the direction of displacement. Reason :- Work done by frictional force can not be positive.

In each of the following a force F is acting on an object of mass m. The direction of displacement is form west to east shown by the longer arrow. Observe the diagrams carefully and state whether the work done by the force is negative, positive or zero.

Work || Kinetic energy

Under what conditionit is wrong to say that an object's acceleration is negative when the object is thrown upward. Does the sign of the acceleration depend at all on the direction. Can an object's acceleration be positive when the object is slowing down ?